Cook pasta shells according to package directions. Drain and rinse in cold water. In a large bowl, combine the next 10 ingredients. Divide the small jar of spaghetti sauce between two ungreased 13x9-in. baking dishes.
Stuff shells with the cheese mixture and place in a single layer over sauce. Pour the remaining spaghetti sauce over shells.
Cover and bake at 350° for 20 minutes. Uncover; bake 10 minutes longer or until heated through.