COOK spaghetti as directed on package, omitting salt.
MEANWHILE, heat dressing and garlic in large nonstick skillet on medium heat. Add chicken and broccoli; cook and stir 5 to 7 min. or until chicken is done. Stir in tomatoes and 1/4 cup mozzarella; cook 1 to 2 min. or until heated through, stirring occasionally.
DRAIN spaghetti; place on serving plate. Top with chicken mixture, remaining mozzarella and Parmesan.