Bring a large pot 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 skillet over medium-high heat. Cook and stir chicken cubes, reducing heat if necessary, until no longer pink in center and juices run clear. Set aside.
In a medium saucepan, bring 2 cups cream to a simmer, stirring often. Whisk in bouillon and cheese until well blended and bouillon has dissolved completely. Dissolve cornstarch 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 skillet over medium high heat. Stir in prosciutto, garlic, and mushrooms and 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.
To serve, place pasta in a large mixing or serving bowl. Add chicken and mushroom mixture and pour in cream sauce. Toss well, and serve.
