1/2 cup softened butter, plus more for baking dish
4 (8 ounce) fillets grouper
1 teaspoon salt
1 tablespoon lemon pepper, or to taste
2 teaspoons garlic powder
2 teaspoons onion powder
1/4 cup key lime juice
1/4 cup fresh orange juice
12 slices lime
Preheat oven to 325 degrees F. Lightly butter a 9x13-inch glass baking dish and set aside.
Season the grouper fillets with salt, lemon pepper, garlic powder, and onion powder; place into prepared baking dish. Spread about 2 tablespoons of softened butter over the top of each fillet. Pour in the lime and orange juices, then cover each fillet with 3 slices of lime, and 2 slices of orange.
Bake in preheated oven until fish is opaque and flakes easily with a fork, about 15 minutes.