Thinly slice the pork and season lightly with salt and pepper.
Prepare vegetables: shred cabbage, slice onion, julienne carrot, and mince ginger and garlic.
Mix soy sauce, oyster sauce, rice vinegar, sesame oil, and cornstarch (if using) in a bowl.
Heat oil in a wok over high heat.
Add pork and stir-fry until browned and cooked through. Remove and set aside.
Add ginger, garlic, and onions to the wok and stir-fry until fragrant.
Add cabbage and carrots, cooking until slightly tender but still crisp.
Return pork to the wok and pour in the sauce mixture.
Toss well until vegetables and meat are coated and sauce thickens slightly.
Taste and adjust seasoning if needed.