Place bread crumbs in a wide, shallow bowl. Whisk together egg and milk In another wide, shallow bowl. Dredge chicken breasts one at a time in the egg mixture first and then in the bread crumbs. Place coated breasts side-by-side in a baking dish.
Dividing evenly, top each breast with 3/4 cup mozzarella and then follow with 1/3 cup parmesan.
Divide spaghetti sauce evenly and spoon over each breast.
Top each breast with remaining mozzarella and parmesan in the same order as above.
Bake for 30 minutes or until juices from chicken breasts run clear and cheese topping is lightly browned.
During last 15 minutes of chicken's cooking time, prepare spaghetti per package instructions.