Cook the quinoa according to the package directions.
Preheat oven to 375 degrees F and lightly grease a 9x13 baking dish or rimmed baking sheet. Brush the halved peppers with vegetable oil and place them cut side up on the baking sheet.
Heat the olive in a medium skillet over high heat. Add the onion and sauté for 5 minutes. Add the cumin, chili powder and garlic powder and stir to combine. Continue to cook for 1 minute and then remove from the heat. Add the spiced onion mixture to the quinoa. Stir in the black beans, cheese, salsa, green onions and corn kernels. Stir to combine and season with salt and pepper as needed. Add more salsa if you want more smokiness.
Generously stuff halved peppers with quinoa mixture until all peppers are full, then cover the dish with foil.
Bake for 30 minutes covered, then remove foil, sprinkle a little extra cheese on top, increase heat to 400 degrees F, and bake for another 15-20 minutes, or until peppers are soft and slightly golden brown.
Garnish with assorted toppings listed above.