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Once they start to turn white, lift up the edges of the omelet with a spatula for a few seconds. This will allow any uncooked egg white to flow underneath and cook. Do this quickly; the egg whites will continue to cook even after you remove them from the skillet. If you want to, you can garnish the omelet further with some diced tomatoes or sun dried tomatoes.
Cook the omelet until the egg whites begin to set. Slide the omelet onto a plate and serve it.