Start by rinsing the quinoa thoroughly under cold water to remove any bitterness. In a medium saucepan, combine the rinsed quinoa with 2 cups of vegetable broth. Bring to a boil, then reduce heat to low, cover, and simmer for about 15 minutes until tender and liquid absorbed. Fluff with a fork and set aside.
Preheat your oven to 375°F (190°C). Cut the tops off the bell peppers and carefully remove seeds and membranes. Lightly brush the outside and inside of each pepper with 1 tablespoon of olive oil. Place peppers upright in a baking dish.
Heat the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add chopped onion and sauté until translucent, about 3-4 minutes. Add minced garlic, cumin, and chili powder, cooking for another minute until fragrant.
Add black beans, corn, and cooked quinoa to the skillet. Stir to combine and cook for 2-3 minutes to meld flavors. Season with salt and pepper to taste. Remove from heat.
Spoon the quinoa mixture into each bell pepper, packing gently but firmly. Fill each pepper all the way to the top.
Cover the baking dish with foil and bake in the preheated oven for 30 minutes. Remove foil, sprinkle shredded cheese over the tops, and bake uncovered for an additional 5-10 minutes until cheese is melted and bubbly.
Remove peppers from oven and let cool slightly. Garnish with fresh cilantro leaves for color and flavor. Serve warm and enjoy!