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 1/3 cup down centre of each taco shell. Divide lettuce, tomato and cheese among tacos. Dollop with yogurt.