Preheat oven to 350 degrees F. Poke the duck all over with a fork. Stuff the onions, garlic and ginger inside the cavity. Fold and tuck the duck wings under the body. Rub the duck with the five-spice powder; tie legs together. Place the duck on a rack in a roasting pan. Pour in cold water until it just reaches just below the duck. Roast the duck 1 hour. Brush with 1/4 of the glaze. Roast 15 minutes more; brush with 1/4 more glaze. Repeat until all the glazed is used and the duck is richly glazed, very tender and you can twist the leg-bone free.
Rest the duck 10 minutes before cutting into portions and arranging on a serving platter.