01 - In a small mixing bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, sesame oil, black pepper, sugar, cornstarch, and cold water until smooth and well combined. Set aside.
02 - Bring a saucepan of salted water to a boil and cook the chow mein noodles according to package directions until al dente. Drain immediately, rinse under cold running water to halt cooking, and set aside.
03 - Heat 1 tablespoon of vegetable oil in a large wok or heavy-bottomed skillet over high heat until shimmering. Add the sliced beef in a single layer and stir-fry for about 2 minutes until just browned on all sides but still tender. Transfer to a plate and set aside.
04 - Add the remaining tablespoon of vegetable oil to the wok. Add the minced garlic, julienned ginger, and sliced onion, and sauté vigorously for about 1 minute until fragrant and the onion begins to soften.
05 - Add the sliced bell peppers to the wok and stir-fry for 2 to 3 minutes, tossing frequently, until they are just tender-crisp and still retain their vibrant color.
06 - Return the seared beef to the wok along with the cooked noodles. Pour the prepared sauce over everything and toss continuously for 2 to 3 minutes using tongs or a spatula until all components are evenly coated and heated through.
07 - Transfer to a serving platter or individual plates, garnish with the sliced scallions, and serve immediately while hot.