Combine beef, oyster sauce, soy sauce, salt, and ground black pepper. Mix and marinate for at least 30 minutes.

Heat a wok and pour-in cooking oil.

Sauté garlic, ginger, and chili.

Stir-fry spinach then place in a serving plate and set aside.

Using the same wok with remaining oil, stir-fry the marinated beef for 5 to 6 minutes or until the color turns brown.

Arrange the beef on top of the spinach.

Serve. Share and enjoy!