Roast the duck breast over wood chips in a smoker for 10 to 15 minutes (place a pan underneath to catch the drippings). Or, place over wood chips on a low fire in a covered grill for 8 to 10 minutes. Remove the skin, remaining fat and dice.
In a wok or large saute pan, heat the canola oil and stir-fry the diced duckmeat, garlic, shallot, onions, choy sum, cilantro, gai choy, water chestnuts, chile flakes, mushrooms, oyster sauce, mint, and basil for 5 minutes over high heat until well combined and cooked through. Drain off the liquid into a saucepan and reduce to a syrupy consistency. Return the reduced liquid to the duck mixture, add the chile sauce, egg yolk and mix well.
Mix 1 tablespoon of the cornstarch and the water together in a small bowl. To make the potstickers, lay out the wrappers on a work surface and place a heaping tablespoon of the filling in the center of each. Moisten the edges of the wrappers with the cornstarch mixture, fold in half and seal the edges. Sprinkle with a little cornstarch to keep them from sticking.
Heat the 1/4 cup canola oil in a cast-iron skillet or heavy-bottomed saute pan. When hot, fry the pot-stickers over medium-high heat for about 1 1 /2 minutes per side or until browned.
To serve, ladle the sauce onto warm serving plates. Place 5 potstickers on each plate in a star shape and garnish with the plum slices from the sauce, if desired, placing 1 slice between each potsticker. Garnish with orange zest, oregano sprigs and sesame seeds.
ORANGE-CHILE PLUM SAUCE
In a saucepan, combine all the ingredients except the plums. Bring to a boil, reduce the heat to low and simmer for 10 to 15 minutes until thickened. Strain and return to a clean saucepan. Add the plums and simmer 5 minutes over low heat.