Cut the tops off the bell peppers and remove the seeds and membranes. Lightly brush the outside of the peppers with olive oil, and place them upright in a baking dish.
In a skillet over medium heat, add the olive oil and sauté the diced onion until translucent, about 5 minutes. Add minced garlic and cook for an additional minute.
Stir in the cooked quinoa, black beans, corn, diced tomatoes, cumin, smoked paprika, chili powder, salt, and pepper. Mix well and let it cook for about 5 minutes, allowing the flavors to meld.
Remove the skillet from heat and stir in half of the shredded cheese.
Spoon the quinoa mixture into each prepared bell pepper, packing it tightly and mounding it slightly on the top.
Top each filled pepper with the remaining cheese.
Cover the baking dish with foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, until the cheese is bubbly and the peppers are tender.
Remove from the oven and let cool slightly. Garnish with fresh cilantro or parsley if desired before serving.
Notes
Feel free to customize the filling with your favorite vegetables.