BROWN meat in large nonstick skillet; drain.
ADD 2 cups water. Bring to boil. Stir in pasta. Reduce heat to medium; cover skillet with tight-fitting lid. Simmer 10 to 15 minutes or until pasta is tender and just a little water remains in the skillet.
STIR in VELVEETA and mushrooms. Cook until VELVEETA is completely melted, stirring frequently. Remove from heat. Stir in sour cream.