SPRAY nonstick skillet with vegetable cooking spray. Heat skillet over medium heat. Add mushrooms, pepper, tomato and onion. Cover and cook until softened. Remove from skillet. Wipe out skillet with paper towel.
SPRAY nonstick skillet with vegetable cooking spray. Heat skillet over medium heat. Add 1/4 cup egg substitute and top with half cooked vegetables. Cook until set but still moist on top, lifting edges of omelet with spatula. Sprinkle with half the cheese and fold in half. Place on 1 bread slice and top with another bread slice. Repeat with remaining ingredients.