01 - Combine sliced chicken with soy sauce, cornstarch, and sesame oil in a bowl. Let stand for at least 10 minutes to tenderize.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, sugar, white pepper, and water in a small bowl until smooth and incorporated.
03 - Prepare noodles according to package directions. Drain thoroughly, rinse under cold water, and toss with 1 tsp oil to prevent sticking.
04 - Heat 1 tbsp oil in a large wok or skillet over high heat. Add marinated chicken and stir-fry until just cooked through, approximately 3–4 minutes. Remove from wok and set aside.
05 - Add remaining 1 tbsp oil to the wok. Sauté garlic and onion for 1 minute. Add carrot, bell pepper, and snow peas; stir-fry for 2–3 minutes until crisp-tender.
06 - Return chicken to the wok. Add cooked noodles, bean sprouts, and spring onions. Pour in the sauce and toss everything over high heat for 2–3 minutes until well combined and heated through.
07 - Transfer to serving plates immediately. Garnish with additional spring onions if desired. Serve with chili oil or extra soy sauce on the side.