See other recipe for Chicken Stock. Preheat oven to 200ºC . Using a sharp paring knife, remove as much of the fat, sinew and translucent membrane as possible from the lamb shanks. Insert garlic slivers into shanks, either by finding natural divisions in the meat or by cutting small incisions. Salt and pepper generously. Arrange lamb shanks in roasting pan, strew on onion slices, and drizzle olive oil over all. Roast in the oven for 25 minutes. Remove the pan from the oven and sprinkle the lamb with oregano, and cinnamon then spoon tomatoes onto the lamb, mounding up the tomatoes on each shank. Pour the white wine around the meat and return the pan to the oven. Roast for an additional 45 minutes. Remove lamb shanks from the pan and set aside. Add chicken stock to the pan, stirring. Stir in the orzo. Arrange the shanks on top of the orzo and baste them with some of the stock. Return the pan to the oven. Cook until pasta is just tender and nearly all of the liquid has been absorbed (about 15 minutes). Remove from the oven, cover pan tightly with aluminum foil, and let stand about 5 minutes. Serve hot with grated cheese.