Gratin doesn't mean "with cheese." It means "it's crunchy on top." That can be from breadcrumbs, from cheese, from both, from neither - my favorite gratin is gratin dauphinois, which can be made with just potatoes and milk: the starch and the milk protein makes a delicate crispy topping after a long bake.
But with lunch today I had Brussels sprouts gratin, which had both cheese and breadcrumbs. It started with quartered sprouts and chopped onions, sprinkled with Old Bay and cayenne:
Top with bread crumbs and a little grated parmesan, pour in a little milk and cream until the level of liquid comes halfway up the sprouts. Bake - I forget what, 350, 375? - until the liquid has reduced and the top is crisp. Super tasty.
Also on the plate, pimento cheese meatloaf and greens (3 parts turnip, 1 part collard, 1 part chicory):