MELT margarine in large saucepan on medium heat. Add onions; cook and stir 3 min. Stir in broth and barley. Bring to boil; cover. Simmer on low heat 25 min. or until barley is tender.
STIR in zucchini, tomatoes and dressing; cook, covered, 10 min., stirring occasionally. Remove from heat.
ADD cheese and basil; mix lightly.