BROWN steak with onion in hot oil in large skillet.
STIR in 1-1/2 cups water, mushrooms and liquid, the bouillon cubes and noodles. Bring to boil. Reduce heat to medium-low; cover. Simmer 10 to 12 min. or until noodles are tender.
STIR in sour cream; cook an additional 2 min., stirring occasionally.