3 large Vidalia onions, sliced
2 Tbsp. butter or margarine
2 cans (10-1/2 oz. each) fat-free reduced-sodium beef broth
1 tsp. chopped fresh thyme leaves
1 cup STOVE TOP Homestyle Herb Stuffing Mix in the Canister
1 cup KRAFT Shredded Low-Moisture Part-Skim Mozzarella Cheese