For the mushroom omelet, cut the mushrooms into slices and fry them in a little oil. Then remove them from the pan.
Mix the egg and pour it into the oiled pan. Move it a little so that the whole bottom is covered.
When the egg is almost set, add the mushrooms and the grated cheese. Leave the whole thing in the pan for a short while and then, using a kitchen aid, beat one half over the other.
Serve the mushroom omelette hot.