Wash the cleaned carp, salt and sprinkle it with some of the crushed black pepper.
Finely chop the onions and sauté them along with the mushrooms in some of the butter, then add some of the finely chopped tomatoes, crushed walnuts, finely chopped parsley, remaining black pepper, wine and salt.
Fill the carp with the mixture, place it in greased baking dish and cover with the remaining slices of tomatoes.
Pour on the remaining melted butter and 1/2 cup water over it.
Bake at moderate temperature until ready.