Preheat oven to 375°F (190°C).
Cut the tops off the bell peppers and remove seeds.
In a large bowl, mix quinoa, black beans, corn, onion, garlic, cumin, chili powder, smoked paprika, salt, and pepper.
Stuff the peppers with the mixture and place them in a baking dish.
Pour salsa over the stuffed peppers.
Cover with foil and bake for 30 minutes.
Remove foil and bake for an additional 10 minutes.
Garnish with avocado and cilantro if desired.