In a bowl, combine sliced beef with soy sauce, oyster sauce, hoisin sauce, and cornstarch. Mix well and let marinate for 15–20 minutes.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add ginger and garlic; sauté until fragrant.
Add marinated beef and stir-fry until browned and cooked through.
Add onion slices and cook until slightly tender.
Toss in green onions and drizzle with sesame oil. Stir-fry for another minute.
Season with salt and pepper to taste.
Garnish with sesame seeds and serve hot with steamed rice or noodles.
