1. Coat a large skillet with cooking spray; place over medium-high heat until hot. Add chicken; brown on all sides. Remove chicken from skillet.
2. Add mushrooms and onion to skillet; cook 2 minutes, stirring constantly. Add chicken, tomato sauce, and next 3 ingredients; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until chicken is done.
3. Meanwhile, cook spaghetti according to package directions, omitting salt and fat. Drain. Serve chicken and sauce over spaghetti.