Cook fettuccine to desired doneness as directed on package. Drain; return to saucepan.
Stir in roast beef, tomatoes, 2 tablespoons reserved tomato liquid, mushrooms and half-and-half. Cook over low heat until thoroughly heated, stirring occasionally.
Stir in cheese. Cook and stir until cheese is melted and sauce is slightly thickened. Stir in parsley. If desired, garnish with additional shredded fresh Parmesan cheese.