1 (7 1/4 oz.) pkg. macaroni & cheese
1 (7 oz.) can tuna, drained
1 (10 3/4 oz.) can cream of celery soup, undiluted
1/2 c. milk
1 tbsp. chopped onion

Prepare macaroni and cheese according to package. Combine remaining ingredients in large bowl; mix well. Stir in macaroni and cheese. Spoon tuna mixture into lightly greased baking dish. Bake at 350 degrees for 18-20 minutes or until lightly browned.