01 - Combine beef slices with soy sauce, cornstarch, sesame oil, and black pepper in a bowl. Mix thoroughly to coat and let marinate for 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 over medium-high heat. Add marinated beef and stir-fry 1–2 minutes until browned. Remove and set aside.
04 - Add remaining oil to wok. Stir-fry garlic, ginger, onion, and bell pepper for 2 minutes until fragrant and softened.
05 - Add snow peas and continue stir-frying for 1 minute.
06 - Return beef to wok. Pour in sauce and toss everything together for 1–2 minutes until sauce thickens and coats all ingredients.
07 - Remove from heat immediately and serve over steamed jasmine rice.