Heat gas or charcoal grill. Sprinkle beef with seasoned salt and pepper. Alternately thread beef, bell peppers and onion onto 6 (12- to 14-inch) metal skewers. Brush beef and vegetables with oil.
Place kabobs on grill. Cover grill; cook over medium heat 8 to 12 minutes, turning once, until beef is desired doneness.
During last 3 to 5 minutes of cooking time, place buns, cut sides down, on grill; cook until toasted.
To serve, spread buns with mustard-mayonnaise spread. Top bottom halves with cheese. Place kabob over cheese in each bun; carefully remove skewer, holding bun firmly around beef and vegetables.