Adjust oven rack to lowest position and heat oven to 450 degrees. Combine zucchini, fennel garlic scallions, basil, wine, salt and pepper in large bowl.
Lay four 14-inch long pieces of foil on work surface. Place one fillet on lower falh of each piece of foil and season with salt and pepper. Top each fillet with one-quarter of vegetable mixture and 3/4 tablespoon butter. Fold foil over fish and vegetables and crimp edges together to form packets.
Arrange packets in single layer on rimmed baking sheet and cook until vegetables are tender and fish is just cooked through, 15 to 20 minutes. Transfer packets to individual plates and cut open with scissors being careful to avoid steam.