Cut the tops off the bell peppers and remove the seeds and membranes. Place them upright in a baking dish.
In a mixing bowl, combine the ricotta cheese, cooked quinoa, chopped spinach, grated Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper. Mix until smooth and well combined.
Spoon the ricotta mixture into each bell pepper, packing it down gently to fill them completely.
Pour the marinara sauce over the stuffed peppers, ensuring they are well coated, and any extra sauce at the bottom of the baking dish is evenly distributed.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the peppers are tender and the cheese is slightly golden.
Remove from the oven and let them cool for a few minutes before serving.
Garnish with fresh basil leaves and serve with additional marinara sauce on the side.
Notes
Feel free to customize the filling with other vegetables or proteins.