Whip the eggs, salt and pepper in a bowl with a fork.
Cut the ham, cheese, and tomato in small pieces.
Cut the onion in thin slices.
Heat up a frying pan with the olive oil.
Pour the eggs in the frying pan, make sure it covers the bottom of the pan.
Add the ingredients in the middle of the eggs.
Fry the omelet so it is almost done on the bottom part. Fold the four edges in toward the middle of the omelet and press them gently down.
Flip the omelet upside down and fry for one minute.
Take the omelet up from the frying pan and place it on a plate with the folded edges upwards so you can see them. Serve it warm directly.