Add quinoa and vegetable stock to a saucepan and bring to a boil over high heat. Once boiling, reduce heat, cover, and simmer until all liquid is absorbed and quinoa is fluffy - about 20 minutes.
Preheat oven to 375 degrees F (190 C) and lightly grease a 9x13 baking dish or rimmed baking sheet.
Brush halved peppers with a neutral, high heat oil, such as avocado oil or refined coconut oil.
Add cooked quinoa to a large mixing bowl and add remaining ingredients - salsa through corn. Mix to thoroughly combine then taste and adjust seasonings accordingly, adding salt, pepper, or more spices as desired.
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, increase heat to 400 degrees F (204 C), and bake for another 15-20 minutes, or until peppers are soft and slightly golden brown. For softer peppers, bake 5-10 minutes more.
Serve with desired toppings (listed above) or as is. Best when fresh, though leftovers keep covered in the refrigerator for 2-3 days. Reheat in a 350-degree F (176 C) oven until warmed through - about 20 minutes.