Lamb Shoulder 1. Preheat the oven to 150 degrees. 2. Rub the lamb with olive oil and spice rub (use 3 tablespoons). 3. Place the lamb on a wire rack in a tray and place 750mls of water in the tray just enough to cover the tray. Roast at 150 degrees for 2 hours, turn down the oven to 120 degrees and roast for a further 6 hours.