Preheat oven to 375°F.
In a medium saucepan, bring the vegetable stock and water to a boil. Add the quinoa or rice and reduce to a simmer. If preparing quinoa, let it cook for 20-30 minutes or until tender. If preparing rice, let it cook for 15-20 minutes or until tender. Set aside.
In a large bowl, combine the cooked quinoa or rice, lentils, spinach, canned corn, cumin, oregano, garlic powder and red pepper flakes. Mix well.
Drizzle the mixture with olive oil and add salt and pepper to taste. Mix well.
Wash the peppers, cut them in half lengthwise and remove the seeds and inside edges.
Scoop the stuffing mixture into the pepper, pressing it down with every spoonful. Continue until the mixture is heaping over the edges. Sprinkle the tops with grated cheese.
Place the stuffed peppers in a 9x13 Pyrex dish and bake for 25-30 minutes or until the cheese is starting to brown and the peppers are cooked through.
Allow the peppers to cool for 10 minutes. Add your desired toppings, pair with a side of greens and/or grains and enjoy!