Heat skillet over medium-high heat coated with cooking spray. Pour in egg mixture. Gently tilt and rotate pan to spread the egg evenly to the edges. I use a small (maybe 9 inch) egg pan, a regular size frying pan will work too but I like the small one.
When egg is almost set on surface but still looks moist, cover one half of the omelet with filling and cheese, to taste. Slip spatula under the unfilled side, fold the omelet in half and slide onto a warm plate.