Preheat the oven to 400°F (200°C).
Cut the acorn squashes in half and remove the seeds.
Place the squash halves cut-side down on a baking sheet.
Roast the squashes for 25-30 minutes until tender.
While the squash is roasting, cook quinoa or rice according to package instructions.
In a skillet, sauté chopped onion and garlic until translucent.
Add diced bell pepper and cook for another 5 minutes.
Stir in black beans, cooked quinoa, cumin, chili powder, salt, and pepper.
Remove the squashes from the oven and flip them over.
Fill each squash half with the quinoa mixture and return to the oven for an additional 10-15 minutes.