1 sm. onion, chopped
1 (8 oz.) jar mushrooms
1/2 c. shredded Cheddar cheese
1/2 (16 oz.) pkg. tater tots
1 can cream of chicken mushroom soup
1/4 c. mayonnaise
1/2 c. sour cream
1 can chopped water chestnuts

Mix all above and put in greased casserole. Bake at 350 degrees for 30 to 40 minutes. I cover dish and uncover last 15 minutes.