How to Make It
Using scissors, cut the cellophane noodles into 3-inch lengths. In a heatproof bowl, cover the noodles with very hot tap water and let stand until clear and pliable, about 5 minutes; drain.
In a large saucepan, bring the stock, scallions, mustard-green pickling liquid, ginger and 1 tablespoon each of rice vinegar and fish sauce to a boil. Simmer over moderately low heat for 15 minutes.
Add the cabbage and simmer over moderate heat for 10 minutes. Add the enoki mushrooms and cellophane noodles and simmer for 3 minutes.
Add the fish to the soup and simmer until barely cooked through, about 2 minutes. Add the cilantro, pickled mustard greens and the remaining 1 tablespoon each of rice vinegar and fish sauce. Serve, passing additional fish sauce and vinegar at the table.