1.Set aside about 8-12-6 of your meatiest pieces of roast duck for topping the soup, and add the remaining duck to a medium pot along with the water and chicken bouillon.
2.Bring the pot to a boil. Once boiling, cover, and simmer for 20 minutes. Meanwhile, prepare the napa cabbage. Trim the ends off the leaves, cut them in half lengthwise, and then cut them cross-wise into 3/4-inch thick strips.
3.Bring a pot of water to a boil for the noodles. Put the pieces of duck on a foil-lined baking sheet. Reheat in the oven at 325°F for 8-10 minutes, and then keep warm in the oven.
4.Once the soup has simmered for 20 minutes, add the napa cabbage, salt, sesame oil, and white pepper. Increase the heat to bring the soup to a simmer again, and then reduce the heat to medium-low and simmer uncovered for another 5 minutes, until the napa is tender.
5.Add the boiling water to a large bowl with the dry noodles. Let the noodles sit for 15 minutes then rinse noodles with cold water and drain.
6.Divide the noodles between four bowls. Add the soup with the boiled duck pieces and the napa to each bowl (top with the meaty roast duck pieces on top). Garnish with cilantro, and serve!