Heat wok and add oil. When the oil is ready, add garlic and chili paste, chili powder or red pepper flakes if using and stir-fry briefly, for about 30 seconds, until the garlic 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 or chicken broth, cover the wok and simmer for about 2 to 3 minutes, until the leaves are dark green and the stalks are tender but not too soft