1. In a small bowl, mix together the drained, flaked tuna, Crosse & Blackwell Lite Mayonnaise, onion and Cheddar. Season to taste with salt and pepper.
2. Butter the bread on one side and then flip the slices over. Pile the filling on two slices of bread (on the unbuttered side) and cover with the remaining two slices, butter side up.
3. Toast the sandwiches in a sandwich press or frying pan and serve piping hot with a green salad and extra mayonnaise.