01 - In a bowl, combine sliced chicken with soy sauce, cornstarch, and sesame oil. Set aside for at least 10 minutes to allow flavors to penetrate.
02 - In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, sugar, ground white pepper, and water until well combined. Set aside.
03 - Prepare noodles according to package instructions until al dente. Drain and rinse under cold water to stop cooking. Toss lightly 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 just cooked through, about 3-4 minutes. Remove from wok and set aside.
05 - Add remaining 1 tablespoon oil to the wok. Add garlic and onion; stir-fry for 1 minute until fragrant. Add carrot, bell pepper, and snow peas; stir-fry for 2-3 minutes until just tender-crisp.
06 - Return chicken to the wok. Add cooked noodles, bean sprouts, and spring onions. Pour in the prepared sauce and toss everything together over high heat for 2-3 minutes until well combined, heated through, and noodles are coated in sauce.
07 - Transfer to serving plates and serve immediately, garnished with additional spring onions if desired.