Preheat the Oven: Preheat your oven to 375°F (190°C).

Prepare the Quinoa: In a medium saucepan, combine the quinoa and vegetable broth (or water). Bring to a boil, then reduce the heat to low, cover, and simmer for about 15 minutes or until the quinoa is fluffy and the liquid is absorbed.

Prepare the Peppers: While the quinoa cooks, cut the tops off the bell peppers and remove the seeds. Lightly brush the outside of the peppers with olive oil and place them in a baking dish.

Mix the Filling: In a large bowl, combine the cooked quinoa, black beans, corn, diced tomatoes, cumin, chili powder, garlic powder, salt, and pepper. Stir until well combined.

Stuff the Peppers: Spoon the quinoa mixture into each bell pepper, packing it gently. If desired, sprinkle cheese on top of the filling.

Bake: Cover the baking dish with foil and bake for 25-30 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the peppers are tender and the cheese is melted and bubbly.

Serve: Remove from the oven and let cool for a few minutes. Garnish with chopped cilantro or parsley, if desired, and serve warm.