1. Sprinkle tilapia with salt and pepper. Place on a broiler pan coated with cooking spray.
2. In a small bowl, combine the yogurt, butter and lime juice. Stir in the onion, olives and seasonings. Spread down the middle of each fillet; sprinkle with feta cheese.
3. Broil 3-4 in. from the heat for 6-9 minutes or until fish flakes easily with a fork. Yield: 8 servings.