1/2 c. chopped onion
2 tbsp. butter
1 can Campbell's cream of mushroom soup
1/2 c. milk
1/2 c. drained, chopped canned tomatoes
2 c. cooked med. noodles
2 cans drained tuna

In saucepan cook onions in butter until tender. Stir in remaining ingredients. Pour into 2-quart shallow baking dish. Bake at 400 degrees for 20 minutes. Top with sliced cheese and croutons if desired. Bake until cheese melts.