CUT each squash piece lengthwise in half; place, cut-sides down, on microwaveable plate. Microwave on HIGH 12 to15 min. or until squash is tender.
MEANWHILE, bring water and margarine to boil in medium saucepan. Add stuffing mix and apples; stir. Cover. Remove from heat. Let stand 5 min.; stir in cheese.
TOP squash with stuffing mixture. Microwave on HIGH 2 min. or until heated through.