Thaw fish fillets, if frozen. Rinse fish; pat dry with paper towels. Sprinkle with salt and black pepper. Measure thickness of fish; set aside.

Preheat broiler. In a small saucepan, combine orange juice, red onion, balsamic vinegar, tarragon, olive oil, garlic, and hot pepper sauce. Bring to boiling; reduce heat. Simmer, uncovered, for 5 to 6 minutes or until reduced to about 1/3 cup. Remove from heat. Remove 2 tablespoons of the liquid; set both mixtures aside.

Coat the unheated rack of a broiler pan with nonstick cooking spray. Place fish fillets on rack. Brush both sides of each fish fillet with the reserved 2 tablespoons liquid. Turn under any thin portions of fish to make uniform thickness. Broil 4 inches from the heat for 4 to 6 minutes per 1/2-inch thickness or until fish flakes easily when tested with a fork.

Meanwhile, for tangerine relish: Peel tangerines and separate into segments. Remove seeds and cut up tangerine segments. In a small bowl, combine chopped tangerines, the remaining orange juice mixture, and the parsley. To serve, divide greens, if using, among serving plates. Top with fish; spoon tangerine relish over fish. Makes 6 servings.