
Prepare the filling. Pour oil into a frying pan. Heat it and add the onion. Cook until golden brown. Transfer the onion to a bowl and mix it with the mushrooms. Season with salt and pepper.

Bake chicken with mushrooms. Line a baking dish with foil. Place chicken fillet on it. Put mushrooms and onions on top and sprinkle with grated cheese. Place in an oven preheated to 180 ˚C for 20 minutes.