01 - Combine beef slices with soy sauce, cornstarch, sesame oil, and black pepper in a bowl. Mix thoroughly and let marinate for at least 10 minutes.
02 - Whisk together oyster sauce, light soy sauce, water, sugar, and cornstarch in a small bowl until smooth. Set aside.
03 - Heat 1 tablespoon vegetable oil in a large wok or skillet over medium-high heat. Add marinated beef and stir-fry for 1–2 minutes until browned. Remove and set aside.
04 - Add remaining oil to the wok. Stir-fry garlic, ginger, onion, and bell pepper for 2 minutes until fragrant and slightly softened.
05 - Add snow peas to the wok and stir-fry for 1 minute.
06 - Return beef to the wok. Pour in prepared sauce and stir-fry for 1–2 minutes until sauce thickens and evenly coats everything.
07 - Remove from heat and serve immediately with steamed jasmine rice.