Pat dry 1 ½ pounds of chicken thighs with paper towels and season with 1 ½ teaspoon of kosher salt on both sides. Transfer them to a large bowl.
Add 2 tablespoons of shawarma seasoning, ¼ cup of lemon juice, ¼ cup of olive oil, and 2 cloves of fresh minced garlic. Mix well using kitchen tongs to coat the chicken with the marinade. Cover the chicken with stretch film and marinate it in the refrigerator for an hour or overnight.
Preheat the oven to 425 degrees F. (218 degrees F.).
Arrange the marinated chicken on the baking sheet on a single layer and place it on the middle rack. Bake for 18-20 minutes or until a meat thermometer inserted into the thickest part of a chicken registers 165 degrees F. If you prefer your chicken shawarma to be on the browned side, move the sheet pan to the top rack and broil for 2-3 minutes (while watching it closely).
Let the chicken rest for 5 minutes, then slice it into ½ inch strips (or you can cut it into cubes as well).
While the chicken is cooking, cook the rice. Into a medium saucepan, add 2 cups of water (or stock), 1 tablespoon of unsalted butter, and 1 teaspoon of kosher salt. Bring to a boil over medium-high heat. Add the rinsed rice, reduce the heat down to low, cover, and cook until rice is tender, about 15-17 minutes. Remove from the heat and let it rest for 10 minutes (do not remove the lid); right before serving, fluff it with a fork and season with black pepper.
To assemble the chicken shawarma bowls, divide the rice among four bowls. Top it off with sliced shawarma chicken, a handful of cherry tomatoes, sliced cucumbers, salad greens, pickled cucumbers, pickled red onions, and a generous dollop of hummus and tzatziki.
Serve right away.