Heat oil in a large frying pan or wok over medium-high heat. Add garlic and ginger. Stir-fry for 30 seconds or until aromatic.
Add the mushroom and stir-fry for 2 minutes. Add the bok choy, corn, oyster sauce and soy sauce. Toss to combine.
Add the water and reduce heat to low. Cover and cook for 2 minutes or until the vegetables are just tender. Serve.