Cook spaghetti according to package directions. Meanwhile, in a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the spaghetti sauce and seasoned salt; set aside.
In a large bowl, whisk the eggs, Parmesan cheese and butter. Drain spaghetti; add to egg mixture and toss to coat.
Place half of the spaghetti mixture in a greased 13-in. x 9-in. x 2-in. baking dish. Top with half of the cottage cheese, meat sauce and mozzarella cheese. Repeat layers. Cover and bake at 350 degrees F for 40 minutes. Uncover; bake 20-25 minutes longer or until cheese is melted.