Prep: 40 minutes
Total: 5 hours
for the focaccia:
5 3/4 cups|825 grams all-purpose flour, plus more for kneading
1 1/2 tablespoons kosher salt
2 teaspoons granulated sugar
1 (1/4-ounce) package active dry yeast
1/2 cup|125 ml extra-virgin olive oil
flaky sea salt
for the sauce:
1 cup|250 grams tahini
1 cup|30 grams firmly-packed basil leaves
1 bunch flat-leaf parsley (2 5/8 ounces), tough stems removed, soft stems and leaves roughly chopped (2 cups|40 grams)
4 teaspoons kosher salt
2 garlic cloves, peeled and roughly chopped
1/2 cup|125 ml fresh lime juice, chilled
1/4 cup|60 ml ice-cold water
freshly ground black pepper
for the vegetables:
12 small Persian cucumbers, halved lengthwise, then thinly sliced crosswise (1 pound 6 ounces|550 grams)
6 celery stalks, trimmed and thinly sliced on a diagonal (8 1/2 ounces|300 grams)
1 bunch radishes, trimmed and thinly sliced (6 ounces|200 grams)
1 large carrot (11 ounces|150 grams), peeled
4 ripe avocados, pitted, peeled, and thinly sliced
juice of 1 lemon
flaky sea salt and coarsely cracked black pepper
1. Make the focaccia: In a large bowl, whisk together the flour and salt. Push all the flour to the side of the bowl to create a deep well. Pour in 2 1/2 cups lukewarm water, then stir in the sugar and yeast. Let stand until the yeast is foamy, about 10 minutes.
2. Using a fork, stir the water and yeast mixture, slowly incorporating the flour, until a sticky dough forms. Cover the bowl with plastic wrap and let the dough rise until doubled in size, either 2 hours at room temperature or 8 hours in the refrigerator.
3. Spread 1/4 cup olive oil over the bottom of a large rimmed baking sheet. Place the dough on the oiled sheet and press it evenly over the bottom of the baking sheet with your fingers. Let stand until puffed, 30 minutes to 1 hour, depending on if the dough is at room temperature or cold from the refrigerator.
4. Heat the oven to 475°F. Uncover the dough and use your fingers to dimple it all over, spacing the dimples about 1 inch from each other. Drizzle the remaining 1/4 cup olive oil over the dough and sprinkle with sea salt. Bake the focaccia until deep golden brown all over, 35 to 40 minutes. Transfer the pan to a rack and let cool for 5 minutes. Using a spatula, lift the focaccia and slide it onto the rack, then let it cool completely.
5. Meanwhile, make the herb sauce: In a blender, combine the tahini, basil, parsley, salt, and garlic, then turn the blender on. While the blender is running, slowly pour in the cold lime juice and 1/4 cup ice-cold water until it emulsifies into a thick spread that has the consistency of mayonnaise. Scrape the sauce into a large bowl.
6. Add the cucumbers, celery, and radishes to the bowl of tahini sauce. Using a vegetable peeler, peel away 2 cups carrot strips and add them to the other vegetables. Stir to coat the vegetables completely in the sauce.
7. Cut the focaccia in half lengthwise, then crosswise into fourths, make 8 rectangles. Split each rectangle like a hamburger bun, leaving it attached along one long side. Scoop the vegetables and sauce onto the bottom half of each sandwich and top with avocado slices. Drizzle with the lemon juice and season with sea salt and coarsely cracked black pepper. Close the focaccia sandwiches, and press lightly to adhere.
8. Wrap each sandwich tightly in a square of foil or parchment paper like a deli sandwich or burrito. Pack the sandwiches in a large plastic container and pack into your cooler for taking to the beach.