1. To make the pickled mustard greens, bring a large pot of water to a boil (you can use it for the pasta afterward). Add the kosher salt. Blanch the mustard greens in the water for 2 minutes.
2. Get a bowl of cold water ready. Plunge the mustard greens into the cold water to stop the cooking. Once cool, drain the greens, squeezing out all the water with your hands. Bunch up the greens and chop into bite-size strips.
3. Put back in the empty bowl, pour the rice vinegar over the top, mix well, and let it sit for 30 minutes while you work on the rest of the dish.
4. To make the pork-shiitake mixture, heat a large skillet or wok over medium-high heat. Add 1 tablespoon of the oil. Add the shiitakes and salt. Panfry the shiitakes until they kick off their moisture and start to brown, about 5 minutes.
5. Add 1 tablespoon of the soy sauce, sugar, and rice wine and simmer until all the liquid evaporates. Transfer the shiitakes to a bowl.
6. Add another 2 tablespoons oil to the pan and then the pork, breaking it up as you fry it. Once all the pink is gone, add the ginger, garlic, the sliced white part of the scallions, and the fermented flour paste. Fry for 1 to 2 minutes.
7. Add the remaining 1 tablespoon soy sauce, mushroom stock, black vinegar, and chili oil. Simmer for 5 minutes, and then keep warm.
8. Squeeze all of the rice vinegar out of the mustard greens and set aside.
9. Cook the noodles according to the package directions. Drain the water from the noodles when they are al dente. Pour the pork-shiitake sauce over the noodles and mix well. Serve each person a portion of noodles, and top with the shiitakes, some pickled mustard greens, and julienned scallions.
10. Drizzle some more chili oil on and around the noodles and serve more at the table.