Lightly flatten each slice of bread with rolling pin, spread thinly with mustard.
Mix tuna, chives, parsley and pepper, spread evenly onto the bread. Roll up each slice and place in a single layer in a lightly sprayed oven proof dish. Beat together milk and egg whites, pour over bread rolls and sprinkle with grated cheese.
Bake in pre-heated oven for 180C for 30 minutes. Cut into portions and serve with salad.