In a large bowl, combine the pork, garlic, Chinese cooking wine, soy sauce, mirin, vegetable oil, ginger, and Chinese five spice. Mix well, then set aside to marinate for 15 minutes.
Toast the Sichuan peppercorns in a small pan over medium heat until fragrant, about 5 minutes, stirring constantly.
Grind the peppercorns with a mortar and pestle or a spice grinder until fine, then add 2-3 teaspoons to a medium bowl. (Add more if you prefer a spicier, tinglier sauce)
Add the chili oil, sesame paste, soy sauce, garlic, sugar, and sesame oil, to the medium bowl and whisk well to form a paste. Set aside.
If using spaghetti pasta, bring a large pot of salted water to a boil and cook the noodles according to the package instructions until al dente. If using fresh noodles, cook for 2 minutes and drain immediately. Do not overcook.
Add the bok choy to the pasta water and blanch for 1 minute. Remove to an ice bath to stop cooking. Drain the noodles and set aside.
Heat a large skillet or wok over medium heat and coat the bottom with oil. Add the prepared meat, and cook, breaking it up with a spatula, until browned and cooked through, about 6-8 minutes.
Stir in the mustard greens and cook for 5 minutes.
To serve, take a serving bowl and add half of the spicy sauce, cooked noodles, cooked pork, 1-2 bok choy, and 2-3 tablespoons of chicken broth. Repeat for the second serving.
Garnish with chopped green onions and crushed peanuts if desired.