To velvet the chicken: In a bowl, add the chicken and sprinkle in the salt. Mix until the salt is fully absorbed. Add the white pepper, sugar, and soy sauce. In a small bowl, combine the cornstarch and water into a slurry, then mix it into the chicken. Add the cooking oil and mix again. Marinate while preparing the remaining ingredients.
To make the sauce: In a bowl, combine the cornstarch and water until smooth. Add the soy sauce, oyster sauce, hoisin sauce, sesame oil, white pepper, and chicken stock. Stir well and set aside.
To prepare the noodles: Bring a pot of water to a boil over high heat. Blanch the Hong Kong pan-fried noodles for about 2 minutes, or until just loosened. Rinse briefly under cold water, drain well, and toss with the cornstarch.
To pan-fry the noodles: Heat the cooking oil in a pan over medium-high heat. Spread the noodles into an even layer and pan-fry for about 3 minutes, or until golden underneath. Carefully flip and cook the second side for another 3 minutes. Transfer to a serving plate.
To cook the chicken: Heat 1 tablespoon of the cooking oil in a wok over high heat. Add the chicken and let it sear briefly before stir-frying for about 3 minutes, or until cooked through. Remove and set aside.
To stir-fry the vegetables: Add the remaining tablespoon of the cooking oil to the wok. Stir-fry the carrots, snow peas, and beech mushrooms for about 1 minute. Add the ginger and garlic and stir-fry for about 10 seconds, or until fragrant.
To finish: Stir the sauce again and pour it into the wok. Bring to a simmer until thickened and glossy. Return the chicken and toss to coat. Spoon the chicken and vegetables over the crispy noodles and serve immediately.