In a small bowl, whisk the egg, egg whites, spinach and pepper sauce; set aside. In a small nonstick skillet coated with cooking spray, saute red pepper and onion until tender. Reduce heat to medium.
Add egg mixture to skillet (mixture should set immediately at edges). As eggs set, push cooked edges toward the center, letting uncooked portion flow underneath. When the eggs are set, sprinkle with cheese; fold omelet in half. Slide omelet onto a plate.