HEAT oil in large saucepan on medium-high heat. Add onions and mushrooms; cook and stir 5 min. or until tender.
ADD eggplant, zucchini, tomatoes and tomato sauce; mix well. Bring to boil; cover. Simmer on medium-low heat 15 to 20 min. or until vegetables are tender.
STIR in stuffing mix just until moistened. Remove from heat. Let stand, covered, 5 min.