Tuna Melt Casserole 12 slices bread (your favorite type) 2 cans tuna, drained 1 small onion, chopped 1/4 cup mayonnaise 6 slices cheese (your favorite type) 1 can cream of chicken soup 1/2 soup can milk Toast the 12 slices of bread. Line the bottom of a 13 x 9-inch baking dish with 6 of the slices and set the other 6 aside. Mix together tuna, onion and mayonnaise and spread on the bread in the baking dish. Place the slices of cheese and the remaining 6 slices of bread on top of the tuna. Finally, mix the soup and milk together and pour over the sandwiches. Bake for 20 to 25 minutes at 350 degrees F.