Melt margarine or butter in a skillet. Pour beaten egg mixture into skillet; reduce heat to low.
With a pancake turner, gently lift the edges as they begin to set and allow uncooked egg to flow underneath.
Continue to cook until mixture is set but top is still moist looking. If desired, spoon filling onto half of the omelet. Loosen the edges with a pancake turner and fold the omelet as you slide it from the pan to a serving dish.