Cut the croissant lengthwise not to the end, so that the croissant would open.
Fry the steak, salt, pepper to taste, let it cool in foil, then cut it lengthwise so that it is thinner, but this is a matter of taste.
Spread one inner side of the croissant with sour cream and mustard, put the steak, the other side is spread with cottage cheese and put the tomato. Done!