COOK pasta as directed on package, omitting salt.
MEANWHILE, cook sausage in large nonstick skillet on medium-high heat 10 min. or until done, stirring occasionally; drain. Return sausage to skillet. Add tomatoes, onions and dressing; stir. Cook 5 min. or until onions are heated through, stirring occasionally.
DRAIN pasta; place in large bowl. Add sausage mixture and 1/2 cup cheese; mix lightly. Sprinkle with remaining cheese.