PLACE steak in freezer 30 minutes to firm. Cut across grain into 2x1/2-inch strips.
MIX sour cream and flour in small bowl. Stir in water, bouillon and pepper; set aside.
MELT butter in large skillet on medium-high heat. Add 1/2 of the steak; cook and stir until steak is cooked through. Remove steak from skillet. Add remaining steak and vegetables to skillet; cook and stir until steak is cooked through and onion is tender. Return all steak to skillet. Reduce heat to medium.
ADD sour cream mixture; cook until bubbly, stirring constantly. Cook an additional minute. Spoon over hot noodles.