HEAT ovenproof skillet on medium heat. Add meat; cook 6 min. on each side or until medium doneness (160ºF). Remove from skillet; cover to keep warm.
MELT butter in same skillet on medium-high heat. Add zucchini and onions; cook and stir 2 min. or until crisp-tender. Transfer to large bowl; stir in stuffing mix and cheese. Add meat to skillet; top with stuffing mixture.
BROIL, 6 inches from heat source, 5 min. or until stuffing is lightly browned.