Toss the pork with dark soy. Heat 1 tablespoon of oil in a wok over high heat. Add the pork and stir-fry for 1 minute. Add the shiitakes, cook for 1 more minute. Add the water chestnuts, and bamboo shoots, cook for 3 minutes. Combine the water, soy sauce, dry sherry, cornstarch, sugar, and pepper, work into a smooth paste. Add to the wok, stir to completely coat. Cook for 2 minutes. Remove from the heat. Add the bean sprouts, green onions, and ginger. Brush your pancakes with a little hoisin. Fill with the pork and vegetables. Roll up and serve.