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.