DIP chicken, 1 breast at a time, in milk, then in grated topping, turning to evenly coat both sides of each breast.
HEAT oil in large nonstick skillet on medium heat. Add onions and garlic; cook and stir 3 min. Add chicken; cook 3 min. on each side. Add tomato sauce, mushrooms and pepper; cover. Simmer 15 min. or until chicken is done (165ºF).
MEANWHILE, cook pasta in large saucepan as directed on package, omitting salt and adding broccoli to the boiling water for the last 2 min.
SPRINKLE mozzarella over chicken; cook 2 to 3 min. or until mozzarella is melted. Drain pasta mixture. Serve with chicken.