1. Preheat broiler.
2. Combine yogurt, lemon juice, garlic, salt and pepper in a small bowl; mix well.
3. Line a broiler pan with foil and place fish on top, skin side down. Spread half the yogurt sauce over fish fillets. Put fish 4 inches under broiler and cook for 10 minutes, or until fish flakes easily with a fork and topping is golden.
4. Serve warm with yogurt sauce on the side.