Prepare the Beef: Heat the vegetable oil in a large stockpot over medium - high heat. Add the beef chunks and sear on all sides until browned, about 5 - 7 minutes. Remove the beef from the pot and set aside.

Make the Broth: In the same pot, add the minced garlic, sliced ginger, scallion knots, star anises, cinnamon sticks, dried chili peppers, and Sichuan peppercorns. Sauté for 1 - 2 minutes until fragrant. Pour in the light soy sauce, dark soy sauce, Chinese five - spice powder, salt, and sugar. Stir well to combine. Return the seared beef to the pot and add 8 cups of water. Bring to a boil, then reduce the heat to low, cover the pot, and simmer for 2 - 3 hours, or until the beef is tender and easily falls apart.

Cook the Noodles: While the beef is simmering, bring a separate large pot of water to a boil. Cook the fresh or dried wheat noodles according to the package instructions. Once cooked, drain the noodles using a colander and rinse them with cold water to stop the cooking process.

Assemble the Dish: Divide the cooked noodles among serving bowls. Ladle the hot beef broth over the noodles, making sure to include several pieces of beef in each bowl. Top the noodles with chopped pickled mustard greens, sliced scallions, and fresh cilantro. Drizzle chili oil over the top according to your preference for spiciness.