Begin by cooking the chow mein noodles according to the package instructions. Drain and set aside, making sure to toss them with a little vegetable oil to prevent sticking.
In a medium bowl, combine the thinly sliced chicken with cornstarch, salt, and a tablespoon of vegetable oil. Mix well and let it marinate for about 10-15 minutes.
In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat. Once hot, add the marinated chicken and stir-fry for about 5-7 minutes, or until cooked through. Remove the chicken from the pan and set aside.
In the same pan, add the remaining vegetable oil. Toss in the minced garlic, sliced celery, and cabbage. Stir-fry for about 3-4 minutes until the vegetables are tender but still crisp.
Return the chicken to the pan along with the cooked chow mein noodles. Add the soy sauce, oyster sauce, sesame oil, and water. Stir well to combine all the ingredients, ensuring the noodles and chicken are well coated with the sauce.
Add the shredded carrots and scallions, tossing everything together for an additional 2-3 minutes. Allow the flavors to meld, and the noodles to heat through.
Remove from heat and serve your Chicken Chow Mein hot, garnished with extra scallions if desired.