Preheat your oven to 375°F (190°C).

Cut the tops off the bell peppers and remove the seeds and membranes from the inside. Place the hollowed-out peppers in a baking dish, standing upright.

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 15-20 minutes, or until the quinoa is cooked and the liquid is absorbed.

While the quinoa is cooking, heat the olive oil in a large skillet over medium heat. Add the diced onion and cook until softened, about 5 minutes.

Add the minced garlic to the skillet and cook for another 1-2 minutes, until fragrant.

Stir in the diced zucchini, tomato, corn kernels, black beans, ground cumin, chili powder, salt, and pepper. Cook for 5-7 minutes, or until the vegetables are tender.

Once the quinoa is cooked, add it to the skillet with the cooked vegetables. Stir to combine and cook for another 2-3 minutes, allowing the flavors to meld together.

Spoon the quinoa and vegetable mixture evenly into the hollowed-out bell peppers, pressing down gently to pack the filling.

If using cheese, sprinkle the shredded cheese over the tops of the stuffed peppers.

Cover the baking dish with foil and bake in the preheated oven for 25-30 minutes, or until the peppers are tender and the filling is heated through.

Remove the foil and bake for an additional 5-10 minutes, or until the cheese is melted and bubbly (if using).

Remove the stuffed peppers from the oven and let them cool for a few minutes before serving.

Garnish with chopped fresh cilantro or parsley, if desired, before serving.