Cut the tops off of the bell peppers and set the tops aside. Remove the inside membranes and seeds and discard. Arrange the peppers cut-side up in a rectangular 9x13 baking dish.
Cook the quinoa. Rinse it well under cold water, then place in a medium saucepan. Add 1 1/2 cups water and bring to a boil over high heat. Once it comes to a boil, reduce heat to low and cover. Simmer until fluffy and the water is absorbed, 15-20 minutes. Remove from heat and set aside.
Dice the onion and the bell pepper from the tops of the peppers. Set a large saute pan over medium heat. When hot, add the olive oil. Add the onion, bell pepper, and oregano and cook, stirring occasionally, until the veggies are tender and the onion is a bit browned, 6-7 minutes.
Remove from heat and stir in the cooked quinoa, black beans, diced tomatoes, corn, green chiles, chili powder, cumin, salt, and pepper.
Divide the mixture between the bell peppers. Carefully add 1/2 cup of water to the bottom of the baking dish and cover the dish tightly with foil.
Bake until the bell peppers are fork-tender, 30 to 40 minutes. Remove the foil and sprinkle with cheese. Bake until the cheese has melted, 5-10 more minutes.
Serve with assorted toppings.
Notes
Cook time includes quinoa cooking time
Meat option:
Add cooked, diced chicken to the mix - about a scant 1/4 cup per pepper.
*Vegan/dairy-free option:
Omit cheese or use vegan cheese.
Note:
The recipe is written so that you'll have ample filling for just about any size bell pepper, so there's a chance you'll have some left over.