Place fillets in an 11- x 7- x 1 1/2-inch baking dish coated with cooking spray. Top fillets evenly with marinara sauce. Arrange cheese evenly over sauce. Sprinkle evenly with Italian seasoning.
Bake, uncovered, at 400° for 15 minutes or until fish flakes easily when tested with a fork. (It's best not to broil this recipe; the cheese may become tough.)