Preheat the oven to 350 degrees F. Poke the duck all over with a fork. Stuff the orange inside the cavity. Fold and tuck the wings under the duck's body. Rub the duck all over with the five-spice powder.
Tie the legs together. Place the duck on a rack in a roasting pan. Pour cold water into the pan until it reaches just below the duck. Cover and roast for 90 minutes. Uncover and roast 30 minutes more.
Baste with the hoisin sauce and roast 10 minutes more, or until the duck is richly glazed. Rest the duck 10 minutes before cutting into portions and arranging on a platter. Serve with hoisin sauce for dipping.