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