Prepare the Vegetables: Prepare napa cabbage, snow peas, sweet peppers, green onion, garlic, and carrot.
Make the Marinade: Mix light soy sauce, oyster sauce, white pepper, corn starch, sugar, and water. Add sliced beef to the marinade and stir.
Prepare the Stir-Fry Sauce: In another bowl, combine light soy sauce, oyster sauce, dark soy sauce, white pepper, sugar, cornstarch, and water.
Stir-Fry the Beef: Heat a wok on the highest setting, add some oil, and stir-fry the marinated beef. Set the meat aside.
Stir-Fry the Vegetables: In the same wok, stir-fry the garlic, napa cabbage, and carrots until they soften.
Combine with Noodles and Sauce: Add par-boiled egg noodles to the wok, mix with the vegetables, then add the stir-fry sauce and pre-cooked beef.
Finish the Dish: Add the remaining vegetables and cook for another 40 seconds. Finish with a drizzle of sesame oil.