Preheat a grill for high heat. Squeeze the juice from 1 lime wedges over fish fillets, then season them with salt and pepper. Grill fish fillets for about 5 minutes on each side, until browned and fish can be flaked with a fork. Remove to a warm serving plate. Heat 1 tbsp oil in a skillet over medium heat. Add 3 cloves garlic, coarsely chopped; cook and stir just until fragrant, about 2 minutes. Stir in 2 tbsp butter, 1 tbsp lime juice and 1/2 cup chopped fresh cilantro. Serve fish with the cilantro butter sauce.