Over low heat, melt the butter in a metal baking dish.
Stir in the lime juice, hot sauce, and garlic powder.
Cut the fillets into 3-inch pieces. (This will make them easier to grill and give them more surface area for the sauce.)
Add fish fillet pieces to the pan and marinate for a few minutes. (Keep the pan warm or the butter will congeal.)
Grill the fish on high heat for about 5 to 10 minutes, basting with the excess marinade as you go. (The melted butter will cause flare-ups on the grill that will help get a nice char on the fish.)
Once the fish is cooked, heat the reserved marinade until the butter is melted, whisk it, and drizzle on top before serving.
Season the fish with salt and pepper to taste.