Preheat your oven to 375°F (190°C).
Rinse the quinoa under cold water. In a saucepan, combine the quinoa and vegetable broth. Bring to a boil, then reduce heat to low, cover, and simmer for about 15 minutes or until the quinoa is fluffy and the liquid is absorbed. Remove from heat.
While the quinoa is cooking, wash the bell peppers, cut the tops off, and remove the seeds and membranes. Place the cleaned peppers upright in a baking dish.
In a mixing bowl, combine the cooked quinoa, black beans, corn, diced tomatoes, olive oil, cumin, chili powder, garlic powder, and season with salt and pepper. Mix well until all ingredients are evenly incorporated.
Stuff each bell pepper with the quinoa mixture, pressing down gently to pack it tightly. Top each stuffed pepper with shredded cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for about 25 minutes.
After 25 minutes, remove the foil and bake for an additional 5 minutes to let the cheese melt and brown slightly.
Remove from the oven and let cool for a few minutes. Garnish with fresh cilantro if desired.