Coat an 8-in. nonstick skillet with cooking spray and place over medium heat. In a small bowl, whisk the eggs, water, salt and pepper. Add half of 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, add half of the red peppers, cheese and onions on one side; fold other side over filling. Slide omelet onto a plate. Repeat.