Mix soy sauce, 2T black tea, peppercorns, and five-spice powder with 3 cups of water.
Remove all visible fat from duck halves. Place duck in non-reactive bowl. Cover with tea mixture and add additional water if necessary to barely cover. Crack walnuts lightly, but leave in shell and add to marinade. Marinate, refrigerated for 24 hours.
Mix half cup black tea, hickory chips, and brown sugar. Put in smoker tray. Smoke-cook duck at 90ºC for about 2 hours or until meat thermometer registers 80ºC at thickest point. Add craked walnuts to the smoker 15 minutes before duck is ready.
Preheat broiler. Remove duck and walnuts. Shell walnuts. Broil duck briefly skin side up to crisp skin if desired. Slice from bone and serve with Chinese plum sauce, mandarin pancakes, whole scallions and smoked walnuts. Serve warm or at room temperature.