First prepare the quinoa on the stove or in an Instant Pot electric pressure cooker.Stove top method: Add the quinoa and 2 cups of water to a 2-quart sauce pan and bring to a boil. Cover the pot and lower the heat to low. Simmer for 15 minutes with the lid on. After 15 minutes, remove the pot from the heat. Instant Pot method: Add the quinoa and 1 1/4 cup water to the Instant Pot. Close the lid and select the Pressure Cook (Manual) button. Set the timer for 5 minutes on high pressure. When the 5 minutes is up, allow the pressure to release naturally. Once the pressure has been released, remove the lid.
Preheat the oven to 375 degrees F.
Meanwhile, heat the olive oil in a large skillet. Add the onions and saute until soft and slightly translucent. Next add the garlic and saute about 30 seconds longer. Then add the bell pepper and saute about 2 more minutes. Finally stir in the chili pepper, cumin, oregano, and salt, to taste.
Remove the skillet from the heat and add the quinoa, black beans, tomatoes, and corn and mix well to combine. Taste and adjust the seasonings, if needed. Stir in half of the vegan cheese.
Transfer the quinoa mixture to a 3 quart (approximately 9 x 13 inch) baking dish. Top the casserole with the remaining vegan cheese.
Cover the baking dish with foil and bake for 20 minutes.
Uncover and bake 10 minutes longer until the casserole is bubbly and the cheese is melted.
Remove from the oven and top with sliced green onions and diced avocado, if desired. Serve with hot sauce tortilla chips on the side, if you like, and enjoy!
Nutrition Facts do not include the optional green onions, avocado, hot sauce, and tortilla chips.Leftovers will keep refrigerated for several days and can be reheated in the oven or microwave.