In a shallow dish combine the salsa, mustard and lime juice. Mix well. Add chicken, toss to coat and then cover and refrigerate. Marinate for at least 30 minutes.
Melt butter in a large frying pan over medium heat. Remove chicken from marinade and fry turning frequently, until browned on all sides.
Meanwhile, simmer remaining marinade in a saucepan for 4 to 5 minutes.
Add marinade to chicken and cook another 3 to 5 minutes or until chicken juices run clear and marinade is starting to glaze. Remove chicken to serving platter; raise heat to high and boil marinade for 1 minute. Spoon marinade over chicken and top each breast with 1 tablespoon yoghurt and 1 lime wedge.