PREHEAT oven to 350°F. Spray large nonstick ovenproof skillet with cooking spray. Heat on medium-high heat. Add chicken; cook 4 minutes on each side or until lightly browned on both sides. Remove from heat. Add vegetables to chicken in skillet; stir gently. Set aside.
ADD milk to flour in deep microwavable bowl; beat with wire whisk until well blended. Microwave on HIGH 8 minutes, stirring with wire whisk every 2 minutes. Add cream cheese spread; beat until completely melted. Add mozzarella cheese; stir until melted. Pour evenly over chicken and vegetables.
BAKE 20 to 25 minutes or until chicken is cooked through. Stir sauce just before serving.