Heat a wok over medium-high heat until a drop of water sizzles and evaporates on contact. Pour in the vegetable oil and swirl to coat the base of the wok.
Season the oil by adding the ginger slice and a pinch of salt. Allow the ginger to sizzle in the oil for about 30 seconds, swirling gently.
Add the mushrooms and stir-fry for 3 to 4 minutes, until they just begin to brown. Add the garlic and stir-fry until fragrant, about 30 seconds more.
Add the bok choy and toss with the mushrooms. The wok/pan may appear crowded, but the bok choy will wilt down quickly. Add the rice wine, light soy, and sesame oil.
Cook for 3 to 4 minutes, tossing the vegetables constantly until they are tender.
Transfer the vegetables to a serving platter, discard the ginger, and serve hot.