Make the sauce: In a small bowl, stir together the sauce ingredients until combined.

Prepare the noodles: In a bowl, soak the noodles in warm water for 15 minutes, then drain them in a colander and place them in a large bowl. Cut the noodles roughly in half with clean kitchen scissors. Add the scallion oil and dark soy sauce, and toss to coat—this will prevent the noodles from sticking to the wok later and add some base flavor.

Heat a wok over medium-high heat until a drop of water evaporates immediately on contact. Add the 2 tablespoons vegetable oil and swirl it around to evenly coat the sides. Add the garlic, white parts of the scallions, shiitake mushrooms, and chilies and stir-fry briefly, about 30 seconds, until the mushrooms are beginning to brown and everything is fragrant. Add the cabbage and toss a few times, stir-frying until itthe cabbage is softened, about 2 minutes. Sprinkle on with the salt and stir to incorporate.

Push the cabbage to one side of the wok. Give the sauce a stir and pour it into the center of the wok. It should sizzle as it hits the hot surface. Immediately add the vermicelli noodles. Stir continuously and fold the noodles to incorporate them with the vegetables and the sauce. If the noodles are cooking too quickly, reduce the heat—you don’t want them to dry out and stick to the bottom. Add more liquid, if needed. When the noodles are piping hot, tender with a slight chew and there isn’t any more liquid visible at the bottom of the wok, remove it from the heat. Stir in the green parts of the scallions, the sesame oil, and ground white pepper (if using). Taste and add additional salt if needed. Serve immediately.