1 can (10 3/4 oz.) condensed cream of celery soup
1 c. milk
1 can (6 1/2 oz.) water-pack tuna, drained and flaked with a fork
1 c. uncooked elbow macaroni
1 c. frozen green peas
1/2 c. chopped onion
1 c. coarsely shredded Cheddar cheese (reserve 1/4 cup)

Whisk soup and milk in a 2 quart microwave safe bowl until well blended. Stir in remaining ingredients except reserved 1/4 cup cheese. Cover and refrigerate at least 12 hours or overnight.

Cover with lid or vented plastic wrap. Microwave on high 15 to 17 minutes until bubbly. Sprinkle with reserved cheese. Let stand uncovered 5 to 7 minutes until cheese melts.