Begin by washing the bok choy thoroughly, ensuring to remove any dirt from the leaves. Trim the base of the bok choy and cut into bite-sized pieces. Set aside.
Clean the mushrooms with a damp cloth and slice them into thin strips.
Heat the vegetable oil in a large frying pan or wok over medium-high heat.
Once the oil is hot, add the minced garlic and ginger, stirring quickly to prevent burning, for about 30 seconds until fragrant.
Add the sliced mushrooms to the pan and stir-fry for about 3 minutes until they begin to soften.
Add the bok choy to the pan and stir-fry for an additional 4–5 minutes or until the bok choy starts to wilt but is still vibrant green.
Drizzle the soy sauce and oyster sauce (if using) over the stir-fry and mix well. Continue to stir-fry for another minute to combine the flavors.
Remove the pan from heat. Drizzle with sesame oil, and season with salt and pepper to taste.
Transfer the stir fry to a serving bowl and garnish with sesame seeds if desired.