Marinate the julienned pork (or chicken thighs) with 2 tablespoons water, 1 teaspoon Shaoxing wine, ¼ teaspoon salt, ½ teaspoon light soy sauce, ¼ teaspoon sesame oil, and ½ teaspoon cornstarch for 15 minutes.
Cook the noodles in a pot of boiling water per the cooking instructions on the package. Drain and set aside. At this point, you can cut the noodles a few times by running a knife or scissors through them so they’re spoon-friendly, but this is optional. The reason for pre-cooking the noodles separately is to prevent the soup from becoming too starchy.
Preheat your wok or thick-bottomed pot until it just starts to smoke. Add 3 tablespoons oil, and cook the marinated meat until it turns opaque. Add the sliced mushrooms and stir-fry for 2-3 minutes.
Add the stock and cooked noodles. Bring to a boil, and lower the heat to a simmer for 5 minutes, until the noodles are softened and expand slightly. Next, add the leafy greens and bring to a boil again. Add salt and white pepper to taste, and sprinkle with the chopped scallion before serving.