Heat the oven. Preheat oven to 350°F. Cut two pieces of parchment paper, approximately 18" wide.
Poach the fish. Combine the wine, water, bay leaf, lemon juice, lemon peel, peppercorns, salt and tarragon in a skillet or sauté pan that has a tight-fitting lid. Heat over medium heat until the liquid is simmering. Add the fish, cover and simmer for 5 minutes. Remove with a slotted spoon.
Make the packets. Divide the fish between the two parchment sheets, place the fish in the center on one side of the parchment. Add the zucchini, squash and shrimp. Sprinkle or spray with a little water then fold the parchment over the fish (like you are closing a book).
Seal the parchment. Start twisting at one end of a side and continue twisting tightly until each side is sealed. Place the packets on a jelly roll pan and bake for 8 minutes.
Make the sauce. Combine the wine, vinegar, lemon juice and shallots in a small saucepan. Heat over medium low heat for 6-7 minutes, until the mixture begins to thicken and reduce. Reduce heat to medium-low and add the butter, one tablespoon at a time. Stir constantly with a whisk after each addition until the butter has completely melted. Repeat until all the butter has been incorporated. Remove from heat and stir in the tarragon.
Serve. When the packets are done, remove them from the oven and cut a slit in the center of each packet. Spoon the beurre blanc sauce over the fish and serve immediately.