Finely chop the mushrooms and garlic.
Heat a little oil in a frying pan, add the mushroom, garlic and thyme leaves and gently sauté until soft. Transfer to a plate.
Whisk the eggs with three pinches of salt.
Heat a little oil in the frying pan, then add the egg and let it spread out. When half cooked, scatter the cheese all over.
When the cheese has melted and the egg has set, scatter the mushroom mixture on the top. Add freshly ground pepper then fold the omelette in half. Cook for another minute or so, then slide it onto a plate.
Serve warm.