01 - Combine sliced chicken with soy sauce, cornstarch, and sesame oil in a bowl. Let sit for at least 10 minutes to tenderize and absorb flavors.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, sugar, white pepper, and water in a small bowl until sugar dissolves completely. Set aside for later use.
03 - Prepare noodles according to package directions. Drain thoroughly, rinse under cold water to stop cooking, and toss with 1 teaspoon oil to prevent sticking.
04 - Heat 1 tablespoon oil in a large wok or skillet over high heat until smoking. Add marinated chicken and stir-fry rapidly until just cooked through, approximately 3–4 minutes. Remove from wok and set aside.
05 - Add remaining 1 tablespoon oil to the wok. Stir-fry garlic and onion for 1 minute until fragrant. Add carrot, bell pepper, and snow peas; cook for 2–3 minutes until vegetables are crisp-tender.
06 - Return chicken to the wok. Add cooked noodles, bean sprouts, and spring onions. Pour sauce over ingredients and toss vigorously over high heat for 2–3 minutes until everything is well coated and heated through. Serve immediately.