Wash the bell peppers under cold water, cut the tops off, remove seeds and membranes, and place them upright in a baking dish.
In a medium saucepan, combine rinsed quinoa and vegetable broth, bring to a boil, reduce heat, cover, and simmer for 15 minutes.
In a large mixing bowl, combine cooked quinoa, black beans, corn, diced tomatoes, cumin, chili powder, garlic powder, salt, and pepper. Mix well.
Stuff each bell pepper with the quinoa mixture, pack it down gently, and sprinkle shredded cheese on top.
Preheat oven to 375°F (190°C), cover baking dish with foil, and bake for 25 minutes. Remove foil and bake for an additional 10-15 minutes until cheese is bubbly and golden.