Prepare food for hot sandwiches. Grate cheese and sausage on a fine grater. Finely chop the onion. Turn on the oven to preheat it.
Cut the bread (longitudinally, in the form of boats), grease with mayonnaise, and tomato (you can do without tomato, as you like). Sprinkle a little cheese, put onions, brush a little with mayonnaise and tomato so that the onions are not dry.
Arrange the sausage and sprinkle with cheese.
Place the sausage and cheese sandwiches in a preheated oven for a couple of minutes at 180-200 degrees.