New Orleans Bayou Burger

1 small green bell pepper, cut into strips
1 small onion, halved, sliced
  Cajun or Creole seasoning mix
1 tablespoon vegetable oil
1/2 cup Ketchup
1 pound lean ground beef
   Sandwich buns

Cook bell pepper and onion in oil until tender; stir in Ketchup and heat briefly. Set aside. Meanwhile, form ground beef into 4 patties; sprinkle both sides generously with seasoning mix. Grill to desired doneness. Serve burgers in sandwich buns, topped with vegetable-ketchup mixture.