1. Combine fennel and shallots in large microwave-safe bowl; cover tightly with plastic wrap. Microwave on high power until fennel has started to wilt, 3 to 4 minutes, stirring once halfway through cooking. Combine butter, zest, garlic, 1 teaspoon tarragon, 1/4 teaspoon salt, and 1/8 teaspoon pepper in small bowl. Combine orange pieces and remaining teaspoon tarragon in another small bowl; set aside.

2. Adjust oven rack to lower-middle position and heat oven to 450°F. Cut eight 12-inch sheets of foil; arrange four flat on counter. Divide fennel and shallot mixture among foil sheets, mounding in center of each. Pour 1 tablespoon vermouth over each mound of vegetables. Pat fish dry with paper towels; season with salt and pepper and place one fillet on top of each vegetable mound. Spread quarter of butter mixture on top of each fillet. Place second square of foil on top of fish; crimp edges together in 1/2-inch fold, then fold over three more times to create a packet about 7 inches square (see illustrations, above). Place packets on rimmed baking sheet (overlapping slightly if necessary).

3. Bake packets 15 minutes. Carefully open foil, allowing steam to escape away from you. Using thin metal spatula, gently slide fish and vegetables onto plate with any accumulated juices. Serve immediately, spooning orange and tarragon mixture over fish before serving.

Serves 4