Rinse the soaked shiitake mushrooms to remove any grit, and thinly slice them.
In a large bowl, add the chicken, mushrooms, water, vegetable oil, sesame oil, Shaoxing wine, oyster sauce, sugar, salt, white pepper, grated ginger, and the white portions of the scallions.
Mix until most of the liquid is absorbed into the chicken. Set the green portions of the scallions aside. Cover the chicken, and marinate for a minimum of 2 hours, or in the refrigerator overnight.
When you’re ready to cook the dish, let the chicken mixture come up to room temperature, and add the tapioca starch (or cornstarch) until it is uniformly incorporated. At this point, all the liquid should be absorbed into the chicken, and there should be little or no standing liquid.
Fill a steamer with enough water to steam continuously for 10 minutes without evaporating (about 3 inches of water is a safe bet). Bring to a rolling boil.
Transfer the chicken mixture to a deep plate or pie dish. Thinly slice the Chinese sausages on an angle, and scatter the slices on top of the chicken.
Carefully place the dish into the steamer, and steam over medium high heat for 10 minutes. Shut off the heat, and leave the chicken in the steamer for another 2 minutes. Sprinkle with green scallions and serve immediately with rice.
Nutrition info calculated with 1 link Chinese sausage.