Mix pork, garlic, ginger, Sichuan peppercorns, red pepper flakes, and cumin in a medium bowl.
Heat oil in a large pot over medium heat.
Add pork mixture; season with salt and pepper and cook, stirring and breaking up with a spoon, until browned and cooked through, 8–10 minutes.
Add broth and bring to a boil; reduce heat and simmer until flavors meld, 8–10 minutes.
Add mustard greens, scallions, soy sauce, and fish sauce and cook, stirring occasionally, until greens are tender, 5–8 minutes; season with salt and black pepper.
Meanwhile, cook noodles according to package directions; drain.
Divide noodles among bowls and ladle soup over.