Cut the tops off the bell peppers and remove the seeds and membranes. Set aside.
In a medium saucepan, combine the quinoa and vegetable broth. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes or until the quinoa is fluffy and the broth is absorbed.
In a large mixing bowl, combine the cooked quinoa, black beans, corn, diced tomatoes, cumin, chili powder, salt, and pepper. Mix well.
Stuff each bell pepper with the quinoa mixture, packing it tightly.
Place the stuffed peppers upright in a baking dish. If they won’t stand, you can slice a small amount off the bottom to level them.
Sprinkle the shredded cheese generously on top of each stuffed pepper.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 10-15 minutes until the peppers are tender and the cheese is bubbly and golden.
Once baked, let them cool for a few minutes before serving. Garnish with fresh cilantro if desired.