Trim fat from steak; slice steak diagonally across grain into thin strips. Cook steak and next 3 ingredients in a large nonstick skillet coated with cooking spray over medium-high heat, stirring constantly, until tender. Drain steak mixture, and set aside; wipe drippings from pan. Melt margarine in skillet over low heat; add flour, stirring with a wire whisk until smooth. Cook 1 minute, stirring constantly. Gradually add 1 cup water, stirring constantly. Add bouillon granules, and cook over medium heat, stirring constantly, until thickened. Stir in salt, pepper, and steak mixture. Cook until thoroughly heated. Remove from heat. Combine cornstarch and sour cream; stir into meat mixture (do not reheat). Serve over noodles.