Wash the baby bok choy and drain. Separate the stalks and leaves. Cut the stalk diagonally and cut the leaves across.
Heat wok and add oil. When oil is ready, add ginger and stir-fry briefly, for about 30 seconds, until the ginger is aromatic. Add the bok choy, adding the stalks first, and then the leaves. Stir in the soy sauce, sugar, and salt, and stir-fry on high heat for 1 minute.
Add the water, cover the wok and simmer for about 2 minutes. Stir in the sesame oil and serve.