Here at Foolproof Living, we love roasting vegetables. If you feel the same way, be sure to also check out our Roasted Eggplant, Roasted Asparagus, and Roasted Butternut Squash recipes and add them into your weekly meal prep.

Roasted red onion slices in a bowl with a spoon on the side.


It’s incredible how delicious food can be with few ingredients and a simple cooking method. You only need a little oil and a pinch of salt and pepper to bring out the flavors while cooking red onions to get that gorgeous caramelization. Here’s what you’ll need:

Ingredients for baking red onions from the top view.
  • Red onions: When you’re at the grocery store, look for large onions that are free firm and free of bruises with their peppery skin still intact.
  • Extra virgin olive oil: I like to use extra virgin olive oil (or another oil with a high smoke point) to get that nice caramelization for your roasted onion slices. Another good option that can withstand high cooking temperatures is avocado oil. 
  • Seasonings: The beauty of this recipe is that you only need a tiny bit of seasoning to get a lot of flavor. Kosher salt and black pepper will do the job of bringing out the natural sweetness of red onions. 

Optional Add-Ins 

You may love the taste of your roasted red onions using only the simple ingredients above. However, there are many great ways to incorporate other ingredients to make this recipe work for whatever you’re cooking it with. Here are some options below:

  • Garlic Powder: Like garlic, onions are part of the allium family. You can season the onions with a dash or two of garlic powder for a savory note. 
  • Balsamic vinegar: Tossing them with a tablespoon of balsamic vinegar is an easy way to infuse them with an even deeper flavor, thereby taking this easy recipe to the next level. Balsamic roasted red onions are especially ideal for topping salads.
  • Spices: You can use a variety of spices for your baked red onion recipe, depending on what you’re making them with. Dried thyme, oregano, and rosemary are good choices for savory dishes. 
  • Brown Sugar: It is optional, but you can add a teaspoon of brown sugar (or coconut sugar) if you want sweeter onions. The sugar will enhance the caramelization and help release more of its juices. 
  • Fresh Herbs: I love finishing a dish with fresh herbs. The brightness of the herbs balances the deep roasted taste of the onions. Try fresh thyme, dill, parsley, or anything else you like.

How To Cook Red Onions in The Oven?

Cooking red onions is so quick, you’ll wonder how you’ve never tried it before. Your new favorite topping will be ready to serve on the dinner table in less than half an hour. Here’s the best way to make this tasty dish:

  1. Preheat the oven: To start, preheat the oven to 400 degrees. Line a rimmed baking sheet with parchment paper, and set aside.
Red onions cut and sliced on a cutting board.
  1. Cut the onion: You have two options when cutting the onion. One is to slice them into rings and keep them whole. The other option is to slice them into rings, cut them in half, and separate them. Remember to peel off the papery skin before slicing. I recommend cutting them into ¼-inch-thick slices for roasting. 
Red onion slices cut and seasoned according to the way they were cut.
  1. Season the onions based on how you cut them: 
    • Cut into rings: If you slice them into rings, place them evenly on your baking sheet. Use a brush to lightly coat them with extra virgin olive oil on each side, and sprinkle them with salt and pepper (optional).
    • Thinly sliced: Separate the red onion slices and place them in a medium-sized bowl. Drizzle with olive oil and sprinkle with salt and pepper. Gently toss them together. Spread them on your sheet pan in a single layer.
Baked red onions after they came out of the oven.
  1. Roast: Place your sliced red onions in the oven. For rings, flip them halfway through, or give them a good stir for thin slices. Cook for about 20 minutes until soft and turned lightly golden brown.
  2. Serve: Take them out of the oven, and let them cool for a few minutes before using them in your recipe.

Storing and Reheating Instructions

We love the fact that baked red onion is a condiment that stores well. Here’s how we store and reheat leftovers:

  • Storing: Let your oven-roasted sliced onions cool to room temperature. Keep them fresh in an airtight container and refrigerate for 3-4 days.
  • Reheating: You can enjoy this recipe either hot or cold, but if you’d prefer it hot, you can reheat it in three ways. 
    • Oven: Put the roasted onions in an oven-proof baking dish with a splash of water. Roast them in preheated 350 degrees F. oven until heated through for about 8-10 minutes.
    • Sautee: Add the red caramelized onions to a saucepan with oil and sautee until thoroughly warmed.
    • Microwave: Place onions in a microwave-safe container with a splash of water. Heat in 30-second increments, stirring each time, until heated through.

How to Use Roasted Red Onions in Your Daily Cooking?

There are countless ways you can use this condiment. The real question is, what don’t they go with? Here are a few uses for red onions:

  • Salads: Caramelized onions pair beautifully with salads, especially if you use cheese in your salads. This La Scala Salad recipe is a prime example. The sweet tang from the onions is absolutely heavenly with feta or goat cheese. You can use butter lettuce or spring mix like in my Goat Cheese and Beet Salad. Another option is to replace the raw red onions in this Friends Salad recipe with cooked red onions. 
  • Pizzas & Taco Topping: Roasting onion to add on top of pizza will please any crowd. They’re also a great topping option for taco recipes like my Black Bean, Quinoa Tacos, and Beef Brisket Tacos.
  • Burgers, Sandwiches, and Wraps: Red onion is a staple for burgers, sandwiches, and wraps, so why not swap them out with its roasted version? Sink your teeth into a Guacamole Bacon Burger or Greek Pita Wraps topped with roasted red onion slices!
  • Cooked Grains and Grain Bowls: Grain bowls are fun because the toppings are limitless. I love adding roasted onions to dishes like my Lemon Quinoa. Have fun with a variation like roasted balsamic onions for this Sweet Potato Quinoa Bowl. They provide the overall dish with a lovely texture and a slightly sweet bite.
  • Dips and salsas: These baked red onions can be the final colorful touch to dishes like Peach Salsa and Pineapple Mango Salsa. 
Oven roasted red onions on a plate with a fork on the side.

Expert Tips:

While the recipe for roasted red onions is pretty straightforward, there are a few things that we’d like to mention so that you can get the best results on your first try:

  • Slice them evenly: It is important that the onion slices are cut evenly (about ¼-inch thickness) to ensure even baking. You can cut them thicker but again, make sure they are even in size.
  • Coat with oil and season well: Take your time when coating the slices with olive oil and seasoning them with salt and pepper. This is an important step in making sure that they are perfectly caramelized and ready to use in recipes.
  • Do not overcrowd the pan: It is important to spread them on a single layer when baking. If you are making this recipe for a crowd (using more onions), we recommend using two baking sheets or cooking them in batches.
  • Flip/Rotate: Do not forget to stir (or flip) the onion slices as they are roasting. Doing so ensures even browning and prevents them from burning.
  • Customize: Feel free to make it your own and customize it to fit the dish you intend to incorporate them into. Enhance the flavors by using various spices and fresh herbs to complement your meal.
Can you roast red onions?

Yes, you can. Roasting red onions may make anyone who doesn’t like onions an onion lover. This is because the baking process softens the pungent flavor of raw onions, bringing out their natural sweetness.

How do you cut a red onion for roasting?

When roasting red onions, you can cut them in two ways:

1- Cut into rings: You can cut the onions into ¼ inch rings or disks. I suggest cutting them this way burgers, sandwiches, or as a side dish. 
2- Thinly sliced: You can also slice them thinly. To do so, cut the onion in half and then slice each half into ¼-inch-thick half-moon slices. Red onion slices are perfect for topping salads, grain bowls, and tacos.

Are roasted red onions healthy?

Cooked red onions have several impressive health benefits. These vegetables are known for their potent antioxidants and healing properties. According to Healthline, they’re loaded with vitamin C and potassium and promote digestive health. So yes, adding a little red onion to your lunch or dinner is an easy way to up the nutritional value of your meals.

How long should I roast onions at 400 f degrees?

Cooking times may vary based on the thickness of your onion slices. However, it takes about 20-25 minutes to cook ¼-inch thick red onion slices in the oven.

Can I use this method for red onion wedges?

Yes, you can. However, depending on the size of your onion, it could take longer to roast them. Use visual cues for doneness. They are done when they are softened, look caramelized, and turned lightly golden browned.

Other Roasted Vegetables You Might Like

If you try this Roasted Red Onions recipe, please take a minute to rate the recipe and leave a comment below. It is a great help to others who are thinking of making the recipe. And if you took some pictures, be sure to share them on Instagram using #foolproofeats so I can share them on my stories.

Roasted Red Onions Recipe

5 from 2 votes
Yields1 cup
Prep Time5 minutes
Cook Time20 minutes
Total Time25 minutes
Roasted Red Onions are a great flavor booster for salads, tacos, sandwiches, and grains. This 3-ingredient vegan recipe also makes a tasty side dish.


  • 1 large red onion
  • 2 tablespoons extra virgin olive oil
  • ½ teaspoon Kosher salt
  • ¼ teaspoon black pepper, optional


  • Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper (or foil) and set it aside.
  • Peel the onions by removing the outer layer and inner papery skin. When cutting, you can either slice them in rings (and keep them whole) or split them into half-moon slices (and separate them.) Either way, for even baking, we recommend cutting them into ¼ inch slices.
  • Season them depending on how you cut them:
    – Cut into rings: Place the red onion rings onto the prepared sheet pan on a single layer. Brush them on both sides with extra virgin olive oil and sprinkle them with salt and pepper (if using.)
    – Sliced thinly: Gently break apart the slices and place them in a medium-sized bowl. Drizzle with olive oil and sprinkle with salt and pepper. Toss to combine. Spread on the prepared baking sheet on a single layer.
  • Roast, flipping (if you are cooking them as rings) or stirring (if you are baking them as thin slices) until softened and caramelized, for about 20 minutes*.
  • Remove from the oven, and let them cool slightly before using in your recipe.


  • Yields: This recipe makes 1 to ½ cups of roasted sliced red onions.
  • Baking time: During the recipe testing, we found out that the roasting time stayed the same for both cutting methods.
  • Storing: Let them cool to room temperature, place them in an airtight container and store them in the refrigerator for 3-4 days.
  • Reheating: You can enjoy this recipe either hot or cold, but if you prefer to serve them hot you can reheat them using one of the three methods below:
    • Oven: Put the leftovers in an oven-proof baking dish with a splash of water. Roast them in preheated 350 degrees F. oven until heated through for about 8-10 minutes.
    • Saute: Add the red caramelized onions to a saucepan with a little bit of oil (or water) and saute until thoroughly warmed.
    • Microwave: Place onions in a microwave-safe container with a splash of water. Heat in 30-second increments, stirring each time, until heated through.
  • Not a fan of red onions? You can use this method/recipe to roast yellow onions as well.


Calories: 293kcal | Carbohydrates: 11g | Protein: 1g | Fat: 28g | Saturated Fat: 4g | Polyunsaturated Fat: 3g | Monounsaturated Fat: 20g | Sodium: 1168mg | Potassium: 168mg | Fiber: 2g | Sugar: 5g | Vitamin A: 5IU | Vitamin C: 8mg | Calcium: 29mg | Iron: 0.5mg

Nutrition information is automatically calculated, so should only be used as an approximation.

Additional Info

Course: Condiment, Vegetarian Side Dish
Cuisine: American
Tried this recipe?Mention @foolproofliving or tag #foolproofeats!

About Aysegul Sanford

Hello Friend! I'm Aysegul but you can call me “Ice." I’m the cook/recipe-tester/photographer behind this site.

If you’re looking for approachable, yet creative recipes made with everyday ingredients, you’ve come to the right place. Here, we’re all about recipes that’s been meticulously tested to provide you with a truly foolproof cooking experience regardless of your level of cooking.

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5 from 2 votes

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Recipe Rating


  1. You’ve got a cup of goat cheese listed in the ingredients right before the 2 ounces of crumbled goat cheese, which tops the salad. Where in the recipe is this other CUP incorporated? I see this is not a new recipe, so I’m surprised nobody else has commented…

    1. Hi Rayann,
      Sadly, it was a mistake from my end. You only need 2 oz. of goat cheese to sprinkle on top at the end.
      I corrected the error. Thanks for bringing it to my attention.

  2. This salad has been on top of my have-to-make-asap list ever since I first opened Plenty More. It looks so tasty and interesting! Now I truly can’t wait to make it and bring some Ottolenghi magic into my kitchen.

    P.S. Happy 2015 <3

    1. Happy new year to you too Sini.
      Ottolenghi’s book is full of wonderful recipes with every day ingredients. I have been cooking from it on a daily basis. I made the orange and date salad today and it was amazing. His creativity literally blows my mind.

  3. Beautifully presented and the flavours sound incredible! I love anything Ottolenghi inspired 🙂 Hope you’re having a great start to 2015 x

    1. Hi Caralyn.. I think so too. And it is so so delicious.
      I made it for Christmas dinner and it was a hit. 🙂

  4. 5 stars
    This is an amazing salad and equally amazing pictures, Aysegul! I am secretly hoping that Santa will buy me a couple of cookbooks for Christmas. Plenty More is on my list.

    1. Ahh Suzy.. You would love this book. I love how his cooking style is so much influenced from the Middle East cooking and flavors.
      There is not one day I am not cooking from that book.
      Happy holidays to you and to your family.

  5. 5 stars
    Hi Aysegul,
    The Walnut Salsa is what drew me to this post oo. It simply sounds amazing and now that I see it, oh my gosh!!!

    Thank you so much for sharing this recipe with us Aysegul. Perhaps after the holidays you will join us for Cookbook Wednesday and little gathering I’ve been having since October where bloggers link their cookbook posts.

    Have a wonderful holiday season and hope to “see” you in 2015. You can reach me at acalenda {at} gmail {dot} com if you have any questions.

    1. Hi Louise..
      I know, right? SO so so delicious.
      Thank you for thinking of me for the cookbook Wednesday project. It sounds so much fun!
      Happy holidays to you and to your family.