Bring a large saucepan of lightly salted water to a boil. Cook pasta for 8 to 10 minutes or until al dente. Drain and set aside.
Heat 2 tablespoons vegetable oil in a frypan over medium-high heat. Cook and stir chicken cubes reducing heat if necessary until no longer pink in centre and juices run clear. Set aside.
In a medium saucepan bring 2 cups cream to a simmer stirring often. Whisk in stock and cheese until well blended and bouillon has dissolved completely. Dissolve cornflour in 2 tablespoons water and whisk into mixture. Cook and stir 2 minutes more then remove from heat and set aside.
Melt butter in a medium frypan over medium high heat. Stir in prosciutto, garlic and mushrooms then cook until mushrooms are tender; about 3 minutes.
Add chicken, reduce heat and continue cooking until chicken is heated through. Return sauce to the stove and add remaining 1/4 cup cream and parsley flakes. Heat through.
Place pasta in a large mixing or serving bowl. Add chicken and mushroom mixture and pour in cream sauce. Toss well and serve.