Combine egg, egg whites, water, salt and pepper in a medium-sized bowl. Beat with a fork until combined but not too frothy.
Spray cooking spray or melt a little butter (1 or 2 tsp) in a skillet over medium-high to high heat.
When the butter stops foaming, pour the egg mixture into the skillet, and allow the eggs to set on the bottom without moving the skillet- this should only take a few seconds.
Take a spatula and push the edges of the egg mixture in, allowing the uncooked eggs on top to flow underneath and make direct contact with the skillet. Repeat the procedure at various spots around the edge of the setting egg mixture.
Place a few tablespoons of filling on one half of the omelet right before it's done, then fold over.
When eggs are set but still shiny, remove the omelette from the heat.