Cook the chow mein noodles according to the package instructions, then drain and set aside.

In a small bowl, mix together the soy sauce, oyster sauce, sugar, salt, and pepper. Set this sauce aside.

Heat 1 tablespoon of vegetable oil in a large skillet or wok over high heat. Add the sliced chicken and stir-fry until it's cooked through and no longer pink. Remove the chicken from the skillet and set it aside.

In the same skillet, add the remaining tablespoon of vegetable oil. Add the sliced onion, bell pepper, garlic, and mushrooms. Stir-fry for a few minutes until the vegetables are tender.

Add the cooked chicken back to the skillet along with the bean sprouts and the cooked noodles.

Pour the sauce mixture over the ingredients in the skillet and stir-fry everything together for a couple of minutes until it's well combined and heated through.

Taste and adjust the seasoning with more salt, pepper, or soy sauce if needed.

Garnish with sliced green onions if desired.

Your chicken chow mein is ready to serve. Enjoy your meal!