Preheat the oven to 400°F (204 °C). Line a baking sheet with parchment paper.
In a small bowl, mix together onion powder, garlic powder, cinnamon, cumin, salt, and pepper.
Brush the insides of acorn squash with olive oil.
Sprinkle each half with the spice mixture, ensuring that it is evenly distributed.
Arrange the squash cut-side down and roast for 40 minutes, or until a knife inserted into the flesh of one of the squash comes out easily. Let it cool on the counter for 5 minutes before stuffing.
While the acorn squash is roasting, make the stuffing. Heat olive oil in a large skillet over medium-high heat. Add the onion and celery, and cook, stirring frequently, until translucent, 5-6 minutes.
Add the apple and cook for 3-4 more minutes, or until the apples are softened.
Stir in the garlic and cook for 30 seconds.
Add the cooked quinoa, cranberries, pecans, and season with salt and pepper. Give it a stir and turn the heat to medium-low. Let it cook for 7-8 minutes, stirring occasionally to ensure it remains moist. If you feel like it is drying, add in a few tablespoons of water.
Taste for seasoning and add more, if necessary. At the last minute, stir in the parsley.
To assemble, fill each roasted acorn squash half with the stuffing and garnish it with pomegranate seeds (if using) and more parsley before serving.