Into a bowl, add only the egg yolks and the salt, mix well until combined.
Into a skillet, add the unsalted butter and, over low heat, grease the entire skillet.
Pour in the egg mixture and let it cook into an omelet.
Cut the mozzarella into small slices and place them on only one side of the omelet, close to the edge.
Now, fold the omelet over the cheese, leaving it in the middle.
Then, in another bowl, place the egg whites. Chop some parsley and add it to the egg whites, mix well.
After that, add half of the egg white mixture to the skillet, right next to the omelet and let it cook for 2 to 3 minutes.
Then fold the egg yolk omelet over the egg white omelet and set aside on the skillet.
Add the rest of the egg whites and let them cook, fold again and transfer to a plate.
Serve.