Begin by cutting the tops off the bell peppers and removing the seeds and membranes. Place them in a baking dish upright.
In a large skillet, heat a drizzle of olive oil over medium heat. Add the chopped onion and garlic, sautéing until softened (approximately 3-4 minutes).
Stir in the quinoa (or rice), black beans, corn, diced tomatoes, cumin, chili powder, salt, and pepper. Mix well and let cook for an additional 5 minutes to heat through.
Remove the skillet from heat and stir in half of the shredded cheese, mixing until melted and combined.
Spoon the stuffing mixture generously into each bell pepper, packing it down slightly as you fill them.
Sprinkle the remaining cheese on top of each stuffed pepper.
Cover the baking dish with aluminum foil and bake for 25 minutes. Then, remove the foil and bake for an additional 10-15 minutes, or until the peppers are tender and the cheese is bubbly and golden.
Once done, let the peppers cool for a few minutes before serving. Garnish with fresh cilantro.
Notes
Feel free to customize the stuffing with your favorite ingredients.