How to Make It
Bring a medium saucepan of water to a boil and fill a bowl with ice water. Using a sharp paring knife, score an “X” on the bottoms of the tomatoes and blanch them in the boiling water for 5 seconds; drain immediately and chill in the ice water. Drain again. Peel the tomatoes. In a small bowl, toss the tomatoes with the shallot, 2 tablespoons of the olive oil and 2 teaspoons of lemon juice and season with salt and pepper. Refrigerate.
Preheat the oven to 400°. In a large bowl, stir the egg whites with the 7 cups of kosher salt, the fennel and 3/4 cup of water until the mixture resembles moist sand. Spread a scant 1/2-inch-thick layer of the salt in an oval baking dish large enough to hold both fish. Pat the salt into a neat oval and place the fish belly to belly, on top. Pack the remaining salt on top of and around the fish. Poke a hole into the crust at the thickest part of the fish, behind the head. Bake for 25 to 30 minutes, until an instant-read thermometer inserted in the hole registers 135°. Transfer the dish to a warm place and let the fish rest for 10 minutes.
Meanwhile, quarter the zucchini lengthwise and cut out the seed cores; discard the cores or save for soup. Cut each quarter into 2-inch pieces. In a small saucepan, combine the zucchini pieces with the remaining 6 tablespoons of olive oil and the garlic and bring to a boil over high heat. Add the 1/2 cup of basil leaves and cook for 1 minute. Transfer the mixture to a blender. Add the remaining 2 teaspoons of lemon juice and 1 teaspoon of kosher salt and pulse to a chunky puree.
Run a serrated knife horizontally around the base of the salt mound and carefully remove the top crust. Transfer the fish to a work surface and fillet them, removing the skin. Transfer to plates. Spoon the zucchini pistou around the fish and garnish with the tomatoes. Drizzle some of the tomato marinade on top and garnish with basil leaves. Serve right away.