Heat the sesame oil in a medium-sized pot over medium-low heat. Add the zha cai, ginger, and whites of the green onion. Saute for 3 to 5 minutes, or until they become fragrant and just start to brown.
Add the vegetable stock and bring to a boil.
Add the bok choy and bring the stock back up to a simmer. Cover the pot and cook until the bok choy is tender, about 5 minutes.
Add the greens of the green onion and a drizzle of sesame oil if desired. Adjust the seasonings to taste with a pinch of sugar, salt, or a splash of the zha cai pickle liquid. (*Footnote 2)
