1 Mix the tuna, red onion, parsley and mayonnaise in a bowl. Season to taste with salt and pepper.
2 Spread four slices of bread with butter and turn around. Cover the sandwiches with the tuna mix and the cheddar cheese and place the other slices of bread on top.
3 Bake the sandwiches in a frying pan without butter on medium heat until the bread is crispy, and the cheese melted.
4 Cut the tuna melt diagonally and serve immediately.