Cook noodles as package directs; drain.

In a large skillet, over medium high heat, cook and stir steak, mushrooms, and onion in margarine until steak is browned and vegetables are tender.

Reduce heat to medium. Add flour; cook and stir for 1 minute.

Add water and bouillon; cook and stir until thickened and bubbly.

Stir in sour cream; heat through. (Do not boil.)

Serve with hot noodles. Garnish with Parsley if desired.