2 tbsp. butter
1/2 c. chopped onion
1 can cream of mushroom soup
1/2 c. milk
2 c. medium egg noodles, cooked
1 c. cooked peas
2 (7 oz.) cans tuna
1/2 c. shredded Cheddar cheese

Combine all ingredients except cheese and pour into 1 1/2-quart casserole.

Bake for 25 minutes at 400°F. Top with cheese and bake another 5 minutes or until cheese is melted.