Cook pasta according to package directions. Meanwhile, in a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Drain pasta; add to meat mixture. , Stir in the tomatoes, relish, mustard, ketchup, steak seasoning and seasoned salt. Bring to a boil. Reduce heat; simmer, uncovered, for 5 minutes. , Sprinkle with cheese. Remove from the heat; cover and let stand until cheese is melted. Garnish with green onions if desired.