In pie plate, arrange fillets in single layer with thicker portions at edge. Brush with lime juice; sprinkle with pinch each of salt and pepper. Cover and microwave at High for 4-6 minutes or until fish flakes easily when tested with fork, rotating dish and rearranging fillets halfway through. Let stand, covered, for 3 minutes. Using slotted spoon, transfer to bowl and coarsely flake fish. Stir in green pepper, onion, salsa and mayonnaise. Taste and adjust seasoning with more salt and pepper. Spoon one third cup down centre of each taco shell. Divide lettuce, tomato and cheese among tacos. Dollop with yogurt.