SAUTE onion and garlic in oil in a large skillet over medium heat until tender. Add sausage and cook, stirring to break up meat, 5 min. or until browned.
ADD tomatoes and spinach; saute for 3 min. Add water; bring to boil. Stir in Shells.
COOK over medium-low heat 14 min. or until Shells are tender, stirring frequently. Stir in Cheese Sauce until well blended.