Start by washing the bok choy thoroughly. Cut the bok choy into quarters lengthwise. Set aside.
Heat the olive oil or sesame oil in a wok or large skillet over medium-high heat.
Add the minced garlic and ginger to the wok. Stir-fry for about 30 seconds until fragrant, being careful not to burn them.
Add the sliced mushrooms to the pan. Stir-fry for about 5 minutes, until the mushrooms are tender and moisture has evaporated.
Add the bok choy to the wok. Stir-fry for another 3-4 minutes until the bok choy is wilted and bright green.
In a small bowl, mix the soy sauce, oyster sauce (if using), and cornstarch (if using). Add this mixture to the wok, stirring well to combine.
Cook for an additional 1-2 minutes until the sauce is heated through.
Season with salt and pepper to taste.
Garnish with chopped green onions before serving.