Preheat oven to 180ºC (355ºF). Place the garlic, lemon rind, pistachio, parsley, mint, salt and pepper in a bowl and stir to combine. Tie the lamb with string and brush with half the oil. Press the pistachio mixture onto the lamb to create a crust and drizzle with the remaining oil. Roast for 10–12 minutes or until the lamb is cooked to your liking. Serve with the celeriac gratin. Serves 12.