In a medium non-reactive bowl combine the chicken with 2 1/2 teaspoons of white sugar, 1 1/2 tablespoons vinegar and 1/4 cup soy sauce. Mix this together and coat the chicken well. Cover and let marinate in the refrigerator for at least 1 hour.
In another medium bowl combine the chicken stock, water, sesame oil and ground black pepper with the remaining sugar, vinegar and soy sauce.
In a separate small bowl dissolve the cornflour with some of this mixture then slowly add to the chicken stock mixture, stirring well. Set aside.
Cook the linguine according to packet directions, drain and set aside.
Heat 1 tablespoon of the vegetable oil in a wok or large saucepan over high heat until it starts to smoke. Add the chicken and stir fry for 4 to 5 minutes or until browned. Transfer this and all juices to a warm plate.
Heat the remaining vegetable oil in the wok or saucepan over high heat. Add the ginger, garlic, mushrooms and spring onions then stir fry for 30 seconds.
Add the reserved sauce mixture and then the chicken. Simmer until the sauce begins to thicken; about 2 minutes.
Add the reserved pasta and toss gently coating everything well with the sauce.