Heat vegetable oil in a pot. Add cinnamon, scallions, garlic, ginger, anise seeds, and chili paste; cook for 1 minute.
Add water, chicken broth, soy sauce, and vinegar. Bring to a boil.
Add beef chunks and simmer gently for 1.5 hours.
Cook noodles separately and set aside.
Add bok choy to the soup and simmer until tender.
Serve the soup with noodles, garnished with cilantro