DIP chicken 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, adding broccoli to 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.