Fry the finely chopped onion in a pan. Cut the mushrooms and fry until golden.
Season the pieces of meat with salt and pepper to taste, spread with cream, and place fried onion and mushroom pieces on top. Cut the tomato into small squares and place on top of the meat.
Place in the oven preheated to 180°C, 5-10 minutes before baking, sprinkle with grated cheese and thyme.