Prepare the Peppers: Preheat your oven to 375°F (190°C). Slice off the tops of the bell peppers and take out the seeds and membranes. Place them upright in a baking dish.
Make the Filling: Heat olive oil in a pan over medium heat. Sauté the diced onion and minced garlic for 2–3 minutes until they soften. Add diced tomatoes, black beans, corn, cumin, paprika, salt, and pepper. Stir well and cook for about 5 minutes.
Mix Everything Together: Mix the cooked quinoa with the sautéed vegetables. Sample the mixture and add more seasoning if required.
Fill the Peppers: Spoon the mixture into each pepper, pressing it down slightly. Sprinkle shredded cheese on top of each one.
Bake: Wrap the dish with foil and bake for 25 minutes. Then, take off the foil and continue baking for another 10 minutes, or until the cheese is melted and golden.
Serve: Garnish with fresh chopped cilantro and serve the peppers warm.