Casseroles can contain about anything you want. Just mix stuff together in a baking dish and put it in the oven. One of my wife's specialties. She makes big ones so we can get three or four meals from one.
With three growing boys and a husband to feed on one income in the '70s, my mom used to make the dreaded tuna noodle. Joke was on everybody else. I liked it. Good, home canned tuna did make it a sight better than some.