Marinate the Chicken: Slice chicken into bite-sized pieces, combine with soy sauce, cornstarch, ground ginger, and garlic powder in a bowl. Mix well and let sit for 15-30 minutes.

Cook the Noodles: Boil salted water, cook noodles according to package instructions until al dente (3-5 minutes), drain, rinse with cold water, and toss with sesame oil.

Stir-Fry the Chicken: Heat vegetable oil in a wok over medium-high heat. Add marinated chicken and stir-fry for 5-7 minutes until cooked through. Remove and set aside.

Stir-Fry the Vegetables: In the same wok, add bell peppers and onions. Stir-fry for 3-5 minutes, then add garlic and mushrooms, cooking for 1-2 more minutes. Add carrots and snow peas, stir for another minute.

Make the Sauce: Whisk together soy sauce, oyster sauce, brown sugar, rice vinegar, and sesame oil. Add red pepper flakes if desired.

Combine Ingredients: Return chicken to wok, pour sauce over everything, and stir to combine. Cook for an additional 2-3 minutes.

Add Noodles: Fold in cooked noodles using tongs or a spatula, ensuring even coating with the sauce.

Serve and Garnish: Transfer to plates, garnish with green onions and sesame seeds, and enjoy immediately.