Pierce the lamb all over with a fork, and then place in a sided dish. Combine all remaining ingredients in a bowl. Brush or rub all over the lamb. Cover and marinate in the fridge 4 hours or overnight, turning occasionally. Preheat the oven to 425 degrees F. Place the lamb in a roasting pan. Pour in 1 cup cold water. Roast 20 minutes. Reduce heat to 325 degrees F and cook lamb to desired degree of doneness, checking its progress with a meat thermometer. 75-90 minutes should yield medium rare in the middle. Baste with pan juices occasionally during cooking. Rest the lamb 10 minutes before slicing thinly.