Start by marinating the pork. Slice the pork loin thin and add it to a bowl with the dark soy sauce, cornstarch or arrowroot, sesame oil, rice vinegar, and white pepper. Toss to coat well and set it aside while you prep everything else.
Next, make the sauce. Add all of the sauce ingredients — the dark soy sauce, oyster sauce, rice vinegar, maple syrup, sesame oil, mirin (if using), chicken broth, and cornstarch or arrowroot — to a bowl and whisk until fully incorporated. Set it aside.
Bring a large pot of salted water to a boil and cook your noodles until al dente, according to the package directions. Drain and set aside.
While the noodles cook, prep your vegetables. Chop the napa cabbage, slice the shiitake mushrooms, cut the green onions into one-inch pieces, and mince the garlic.
Heat the avocado oil in a large skillet over medium heat. Add the marinated pork along with any remaining marinade and cook, stirring occasionally, until the pork is cooked through.
Add in the cabbage, mushrooms, and green onions and stir until wilted and tender, about two to three minutes.
Add in the cooked noodles and pour the sauce over everything. Toss to coat very well, making sure every noodle gets covered in that gorgeous sauce.
Remove the pan from the heat, plate, and enjoy! Store any leftovers in an airtight container in the fridge for up to three days.