Slice the beef thinly and marinate it with soy sauce and cornstarch for 15–20 minutes.
Heat oil in a wok or skillet and stir-fry the beef until browned. Remove and set aside.
In the same pan, sauté minced garlic, grated ginger, and sliced red chilies until fragrant.
Add soy sauce, oyster sauce, and a splash of water, then simmer for 2–3 minutes.
Return the beef to the pan and toss until evenly coated with the spicy garlic sauce.
Stir-fry for another 1–2 minutes until everything is well combined.
Garnish with sliced green onions or sesame seeds and serve hot with steamed rice or noodles.