1. Preheat barbecue to a medium heat. Place 1 tablespoon oil, lime juice and black peppercorns in a bowl and mix to combine. Brush oil mixture over fish and marinate at room temperature for 10 minutes.
2. Brush potatoes with oil and sprinkle with salt. Place potatoes on lightly oiled barbecue grill and cook for 5 minutes each side or until tender and golden. Move potatoes to side of barbecue to keep warm.
3. Place fish on lightly oiled barbecue grill and cook for 3-5 minutes each side or until flesh flakes when tested with a fork. To serve, arrange potatoes attractively on serving plates and top with fish.