Original: Examples of casseroles prepared in this manner are tuna casserole (with canned tuna, cooked pasta, sometimes peas, and cream-of-mushroom soup) and green bean casserole (green beans with cream of mushroom soup, topped with french fried onions). A similar staple food, macaroni and cheese, can also be prepared as a casserole.
Simplified: A very popular type of casserole is green bean casserole, which has green beans, milk or cream, and fried onions.