To marinate the chicken, in a bowl, combine the chicken with the salt, then add the white pepper, rice wine, egg white, and cornstarch and mix well, then add the cooking oil and mix again to coat. Let marinate while preparing the other ingredients.
To cook the noodles, in a pot of boiling water over high heat, add the noodles and cook for about 20 seconds until just al dente, then rinse under cold water and drain well.
To make the sauce, in a bowl, combine the soy sauce, dark soy sauce, oyster sauce, water, and white pepper and mix well.
To cook the chicken, in a wok over high heat, add 2 tablespoons of the cooking oil, then add the chicken and stir-fry until cooked through, then add the garlic and stir-fry briefly and remove.
To cook the vegetables, in the same wok, add 1 tablespoon of the cooking oil, then add the onion, snap peas, mushrooms, and carrot and stir-fry briefly until aromatic, then remove.
To stir-fry the noodles, in the wok, add the remaining 1 tablespoon cooking oil, then add the noodles and let them sit briefly before tossing to lightly sear.
To combine, return the chicken and vegetables to the wok, then add the sauce and toss everything together until evenly coated, then add the bean sprouts and scallions and toss briefly.
To serve, transfer to a plate and serve immediately.