01 - In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, sesame oil, black pepper, sugar, cornstarch, and water until smooth. Set aside.
02 - Prepare the chow mein noodles according to package directions. Drain well, rinse under cold running water to halt cooking, and set aside.
03 - Heat 1 tbsp of vegetable oil in a large wok or heavy-bottomed skillet over high heat until the oil just begins to smoke. Add the sliced beef in a single layer and stir-fry for about 2 minutes until browned on all sides but still slightly pink inside. Transfer to a plate and set aside.
04 - Add the remaining 1 tbsp of vegetable oil to the wok. Add the minced garlic, julienned ginger, and sliced onion. Stir-fry for 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 until crisp-tender and lightly charred at the edges.
06 - Return the seared beef and any accumulated juices to the wok. Add the cooked noodles and pour the prepared sauce over everything. Using tongs or a spatula, toss continuously for 2 to 3 minutes until all components are evenly coated and heated through.
07 - Transfer to a serving platter, scatter the sliced scallions over the top, and serve immediately while hot.