Firstly, in a bowl, combine the thinly sliced chicken breasts with soy sauce, cornstarch, and vegetable oil. Mix well to ensure the chicken is evenly coated and let it marinate for at least 15 minutes. This step is essential for tenderizing the chicken and infusing it with rich flavors.

Meanwhile, prepare the Chow Mein sauce. In a small bowl, mix together the soy sauce, oyster sauce, hoisin sauce, dark soy sauce, sesame oil, sugar, and ground white pepper. Stir until the sugar is dissolved and the ingredients are well combined. Set aside the cornstarch slurry for later use.

Next, cook the egg noodles according to the package instructions until they are al dente. Drain the noodles and rinse them under cold water to stop the cooking process. This helps to prevent the noodles from becoming mushy. Toss the noodles with a little vegetable oil to prevent them from sticking together.

Then, heat a large wok or skillet over high heat and add 1 tablespoon of vegetable oil. Once the oil is hot, add the marinated chicken and stir-fry until it is fully cooked and lightly browned. Remove the chicken from the wok and set it aside.

In the same wok, add the remaining vegetable oil. Add the sliced onion and minced garlic, stir-frying until fragrant. Then, add the shredded cabbage, julienned carrots, bean sprouts, sliced green onions, and bell pepper. Stir-fry the vegetables until they are tender-crisp, about 3-4 minutes.

After that, return the cooked chicken to the wok with the vegetables. Add the cooked noodles and pour the prepared Chow Mein sauce over the top. Gently toss everything together to combine. Add the cornstarch slurry to the wok and stir continuously until the sauce thickens and coats the noodles evenly. Drizzle the final dish with sesame oil.

Finally, once everything is well combined and heated through, transfer the Chicken Chow Mein to a serving platter. Garnish with additional sliced green onions if desired. Serve immediately and enjoy the authentic taste of homemade Chicken Chow Mein.