Cook noodles according to package directions; drain.
Meanwhile, in a large saucepan combine broth, fish sauce, cinnamon, ginger, and, if desired, star anise. Bring to boiling; reduce heat. Simmer, covered, for 5 minutes. Add green onions; simmer, uncovered, for 5 minutes. Add chicken; simmer, uncovered, for 1 minute more. Remove and discard cinnamon and star anise.
Divide cooked noodles among soup bowls. Ladle broth mixture over noodles. Serve with bok choy (if desired), herbs, jalapeno peppers (if desired), and lime wedges.