Step 1

In a large pot, bring 4 quarts of water to a boil. Add the noodles and cook until tender, 5 to 6 minutes. Reserve 1 cup of the cooking water, then drain the noodles and rinse under cool water until cold. Drain well, then set aside in the colander.

Step 2

In a 12-inch skillet over medium-high, heat the oil until shimmering. Add the mushrooms and sauté until softened and the bits clinging to the bottom of the pan begin to brown, about 3 minutes. Add the pork and cook until crispy and caramelized, about 6 minutes.

Step 3

Stir in the minced scallions, garlic and pepper flakes, then cook until fragrant, about 1 minute. Add the sherry and cook, scraping the pan, until evaporated. Stir in the reserved cooking water, black bean sauce, hoisin and soy sauce. Bring to a simmer and cook over medium, stirring occasionally and breaking up any large bits of pork, until the sauce has the consistency of thin gravy, 4 to 5 minutes. Off heat, stir in 2 tablespoons of the vinegar.

Step 4

While the sauce simmers, season the cucumbers with the remaining 1 teaspoon of rice vinegar. Divide the noodles among serving bowls, then spoon the sauce over them. Top with sliced scallion greens and cucumber.