Slice the beef across the grain into thin strips, approximately ⅓ inch (8 mm) thick. Place the slices into a bowl. Add the light soy sauce, cornstarch, baking soda, salt, and water. Using your hands, mix and massage the liquid into the beef until fully absorbed. Add the cooking oil and stir to coat evenly. Let the beef marinate for 15 minutes.

In a small bowl, combine the oyster sauce, Shaoxing rice wine, light soy sauce, dark soy sauce, cornstarch, sugar, ground white pepper, and water. Stir thoroughly, then add the sesame oil. Set the sauce aside.

Heat 2 tablespoons of oil in a wok or skillet over medium-high heat. Add the marinated beef, spreading the strips into a single layer. Let the beef sear undisturbed until the side in contact with the pan develops a light brown crust. Stir and toss the beef for about 30 seconds until the outside is no longer visibly pink. Do not overcook. Transfer the beef to a plate, leaving any remaining oil in the wok.

Add the remaining ½ tablespoon of oil to the wok. Toss in the sliced onion and garlic, frying over high heat until the garlic develops golden edges. Add the bell peppers and stir-fry for about 30 seconds, ensuring they are well heated but still retain their crunch.

Return the beef to the wok, mixing it with the vegetables. Stir-fry for another 30 seconds, ensuring the beef is fully cooked with no visible pink inside.

Reduce the heat to low. Stir the prepared sauce to ensure all ingredients are well combined, then pour it over the meat and vegetables. Toss everything together until the sauce thickens and evenly coats the ingredients. Serve immediately once the dish is glossy and aromatic.