In a small bowl, combine the olives, capers, lemon juice, oil, yogurt, dill or parsley and pepper.
Stir or whisk until well blended. Set aside while you prepare the fish.
Coat a large nonstick frying pan with nonstick cooking spray and place over medium heat. When hot, place the fish fillets in the pan and cook, turning once, until the fillets are well browned and opaque throughout, about 4 minutes on each side.
Transfer fillets to individual plates. Spoon the relish evenly over the fish and garnish with lemon wedges and dill or parsley sprigs.