Crack the entire eggs and pour the content into a bowl.
Add salt and pepper and whisk till it gets fluffy.
Melt the butter in frying and add the chopped onions and mushrooms.
Cook till the mushroom softens and the mixture is translucent.
Add the whisked egg in the pan and cook at medium heat.
Spread the shredded cheese on the eggs evenly once the egg starts to solidify.
Fold the omelets in half with a spatula and allow to cook for a few minutes before removing from heat.