Place a slice of bread on a plate and top with the sliced mozzarella and sliced tomato. Place the other slice of bread on top to make a sandwich.
Beat the egg in a bowl with a little salt and freshly ground black pepper. Dip the sandwich into the beaten egg.
Heat the olive oil in a pan, add the sandwich and fry for 2-3 minutes on each side, or until golden-brown. Remove from the heat, cut in half and serve on a plate.
