HEAT oven to 375ºF.
MIX cream cheese, spinach, 1 cup mozzarella and 3 Tbsp. Parmesan until blended; spread onto chicken. Starting at one short end of each breast, roll up chicken tightly. Secure with wooden toothpicks, if desired.
BEAT egg in shallow dish. Mix remaining Parmesan and cracker crumbs in separate shallow dish. Dip chicken in egg, then roll in crumb mixture to evenly coat. Place, seam sides down, in 13x9-inch baking dish sprayed with cooking spray.
BAKE 30 min. or until chicken is done (165ºF). Remove and discard toothpicks. Serve chicken topped with spaghetti sauce and remaining mozzarella.