Season the pork with salt and pepper. Heat a skillet over medium-high heat with the vegetable oil. Add the pork and brown on all sides, 6 to 8 minutes. Transfer to a plate.
Combine the broth, soy sauce, sherry, sugar, sesame oil, red pepper flakes, star anise and cinnamon stick in a 5-quart slow cooker. Stir to dissolve the sugar, then add the garlic, ginger and mushrooms. Add the pork, cover and program to cook 4 hours on high, then 2 hours on low, or 6 hours total on low.
Transfer the pork to a platter, cover and let rest 15 minutes. Remove the mushrooms from the broth and halve them, then return to the broth.
Meanwhile, bring a large pot of salted water to a boil and cook the noodles as the label directs. Slice the pork. Divide the noodles among bowls and top with some of the broth and mushrooms and a few slices of pork. Garnish with the water chestnuts, chiles, scallions and cilantro.