Heat the oil in a skillet over medium heat. Add in the onion garlic, and taco seasoning. Cook for 3-4 minutes until softened.
In a large bowl, mix together the onion mixture, quinoa, black beans, corn, salsa, green chiles, and cheese.
Divide the mixture between the bell peppers and place in a baking dish. Cover with foil and bake for 20 minutes. After 20 minutes, remove the foil and continue baking an additional 20 minutes. Top with optional toppings and serve.