Preheat the grill.
Lay the grouper on a large piece of aluminum foil. Cover the grouper, inside and out with the lemon and lime wedges, orange and onion slices. Drizzle the fish with olive oil and season with salt and pepper. Wrap the aluminum foil around the fish. Place the fish on the grill and grill for 10 minutes, flip and grill for another 10 minutes, or until the meat is opaque and cooked through.
In a bowl, toss together the tomatoes and onion. Drizzle with olive oil and season with salt and pepper. Serve the tomato salad on top of the grouper.
Yield: 4 servings