Preheat barbecue to high heat. Cut lamb into 2, 4 rib racks and trim away excess fat. Brush meat side with olive oil. Place salt, pepper, rosemary and mint on a plate. Press meat side of the racks into this mixture, pressing it on to coat. Place the lamb bone-side down on one side of the barbecue. Turn the heat off underneath it. Turn the other side to medium-high. Close the lid and cook 9-10 minutes, turn the lamb, meat side down and cook 9-10 minutes more. The lamb should now be cooked medium rare with an internal temperature of 130 degrees F. (Check with an instant read thermometer.) Cook the meat longer if you like it more well-done or if the racks are thick. Rest the lamb 5 minutes to allow the juices to set before serving.