Grouper is a dense whitefish, not oily like mackerel. So you can do anything with it that you'd do with say, cod, or snapper.
It's great in Oriental dishes like steamed w/black bean sauce, or cut in thin slices and made into tempura.
My Hawaiian Aikido sensei makes a baked version -
SENSEI'S BAKED FISH
Fish steaks like grouper or mahi-mahi
Panko bread crumbs
Lemons or limes
Preheat oven to 350. Salt and pepper fish and place in a buttered baking dish. Spread a layer of mayonnaise over the top of the fish; then sprinkle bread crumbs over top; squeeze juice of lemon or lime over and drizzle with melted butter. Bake til fish is flakey and done.
Because it's a mild fish, it will take well to just any type of seasoning you want to use on it - Italian, Mexican, Oriental, etc. It's one of our 'local' fishes here in Charleston, and all the restaurants have some version of it on their menus.