Spread the tomato purée on one side of each slice of bread and sprinkle with oregano.
Place a handful of grated cheese in the middle of each sandwich with the tomato sauce on the inside and top with salami.
Put the slices of bread together to make a sandwich. Brush the outside of each sandwich with butter and cook at Gas 5/190°C/375°F for 5 to 10 mins or grill until the cheese melts.