Cook the chow mein noodles according to package instructions. Drain and set aside.
In a bowl, mix together the soy sauce, oyster sauce (if using), cornstarch, chicken broth, sesame oil, sugar, and ground white pepper to create the chow mein sauce. Set aside.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add the sliced chicken and stir-fry for about 5-7 minutes until cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add minced garlic and onion. Stir-fry for 2 minutes until fragrant.
Add the bell pepper, carrots, and bean sprouts to the skillet, and stir-fry for another 3-4 minutes until the vegetables are tender-crisp.
Return the cooked chicken to the skillet, then add the prepared chow mein sauce. Toss everything together and cook for an additional 2-3 minutes until heated through and the sauce has thickened.
Add the cooked chow mein noodles to the skillet, tossing to combine thoroughly with the chicken and vegetables. Cook for one more minute.
Remove from heat and serve hot on individual plates.