Wash the mushrooms well, cut them in two or four depending on the size, then sprinkle with lemon juice.
Peel the onion and garlic and chop finely. If they are fresh, peel and chop the tomatoes.
Heat the mushrooms in hot oil over high heat, stirring constantly. Add the onion, garlic and chopped rosemary and cook a little longer, then add the tomatoes, season with salt and pepper and simmer for 10 minutes. If necessary, it can be filled with 50 ml of water, depending on how much sauce the tomatoes leave.
It can be served as a garnish for steaks, but it is just as tasty and served as a main course with toast.