Turn instant pot to sautee setting, heat oil. Add the cubed beef, sear on all sides and remove. Add the ginger, garlic, saute for a minute. Add the chopped onions, saute until translucent, about 3 minutes. Add chili bean paste, stir for 30 seconds.
Add 9 cups of water, whole green onions, 2 tablespoons salt, star anise, rock sugar, soy sauce. Add back the beef. Put the peppercorn in a cheesecloth, add to the pot.
Close and lock the lid of the IP. Set the knob to seal. Press Pressure Cook for 23 minutes. Let natural release for 20 minutes. Cover the knob with a kitchen towel (to avoid getting burned) and use a utensil to manually release remaining steam.Carefully open the lid. Cancel the keep warm option. Set to sautee to boil the broth. Add the tomatoes. Taste the broth and adjust seasoning, by adding more salt or more sugar if necessary. Meanwhile, cook the noodles according to package instructions. Drain the noodles and divide into 4 large bowls. Wash and trim the bok choy and put in each bowl.
Slice the pickled mustard greens and put in each bowl. Spoon the beef and broth into each bowl. Garnish with green onion and coriander. Serve piping hot.