Whisk egg substitute, Cheddar cheese, Parmesan cheese, salt, black pepper, garlic powder, and red pepper flakes together in a bowl.
Heat olive oil in a nonstick skillet over medium heat; cook and stir mushrooms and onion until tender, 4 to 5 minutes. Add spinach; cook until spinach wilts, 3 to 4 minutes. Pour in egg mixture; swirl pan around to evenly distribute egg mixture. Cook until egg is fully cooked and set in the middle, 5 to 10 minutes. Cut into wedges.
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.