Cut the tops off the bell peppers and remove the seeds and membranes. Lightly season the insides with salt and pepper. Place them upright in a baking dish.
In a medium saucepan over medium heat, combine the quinoa and vegetable broth. Bring to a boil, then reduce heat to low, cover, and simmer for about 15 minutes or until quinoa is fluffy and the liquid is absorbed.
In a large skillet, heat a drizzle of olive oil over medium heat. Sauté the diced red onion for 3-4 minutes until softened. Add minced garlic, cumin, chili powder, and smoked paprika. Continue to cook for another minute until fragrant.
In a large bowl, combine the cooked quinoa, sautéed onion mixture, black beans, corn, halved cherry tomatoes, and chopped cilantro. Mix until well blended. Adjust seasoning with salt and pepper as needed.
Spoon the quinoa mixture into each of the prepared bell peppers, packing it in gently. If using cheese, sprinkle it on top of each stuffed pepper.
Cover the baking dish with foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes, or until the peppers are tender and the cheese is bubbly.
Once done, remove from oven and let cool for a few minutes. Garnish with sliced avocado and additional cilantro before serving.
Notes
Feel free to customize the toppings and spices to your preference.