Grease a 9×13-inch baking dish and pour pasta sauce into dish. Stir in ¼ cup parmesan. Add chicken into dish and turn to coat chicken evenly in sauce. Cover dish with oven-proof lid or foil.
Bake 30 minutes or until chicken reaches internal temperature of 165 °F.
Meanwhile, cook spaghetti according to package directions.
When chicken is fully cooked, top with mozzarella cheese and remaining parmesan cheese. Bake for 5 minutes, uncovered, until cheese is melted.
Serve the chicken parmesan over cooked spaghetti and spoon on extra sauce, as desired.