Place steak in freezer 30 minutes to firm. cut across grain into 2x1/2-inch strips.

Mix sour cream and flour into 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