½ pound ground pork
2 cloves garlic finely chopped
2 teaspoons finely grated peeled ginger
1 teaspoon Sichuan peppercorns, crushed
¾ teaspoon crushed red pepper flakes
½ teaspoon cumin seeds, coarsely chopped
1 tablespoon vegetable oil
Kosher salt and freshly ground black pepper
4 cups low-sodium chicken broth
1 bunch mustard greens, torn
4 scallions, thinly sliced
2 tablespoons reduced-sodium soy sauce
1 teaspoon fish sauce
8 oz. wide rice noodles
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.