Wipe the mushrooms with a damp cloth, cut them.
Peel the onion and slice it.
In a frying pan, pour vegetable oil, heat, put the chopped onion, fry until transparent.
Add the chopped mushrooms, fry until the mushrooms are ready
Put the roast in a cup and let it cool.
Cut the cheese into small cubes, add to the mushrooms. (Good combination with smoked cheese.)
Mix sour cream with tomato paste, stir
Season the mushroom filling with sauce, salt and pepper. If there is a mushroom powder, you can add it to the filling to enhance the taste.
Put the filling on the bread.