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