1Heat gas or charcoal grill. In small bowl, mix relish ingredients; cover and refrigerate until serving.
2In another small bowl, mix mustard and oregano; set aside.
3Place sausages on grill over medium heat. Cover grill; cook 10 minutes, turning occasionally. Continue grilling 8 to 10 minutes longer, turning and brushing occasionally with mustard mixture, until no longer pink in center. Discard any remaining mustard mixture.
4Serve sausages on buns with relish.