Pan bagnat: Summer vegetable sandwich with tuna

For the rolls

A double recipe of Olive Oil Bread Dough, allowed to rise until doubled in size, or 4 or 6 store-bought crusty buns (6 buns measuring about 5 inches/12 cm across or 4 measuring about 6 inches/15 cm across)
Flour for the work surface

For the filling

3 large eggs, at room temperature (optional)
1 garlic clove, cut in half (optional)
6 tablespoons 90 ml extra-virgin olive oil
Red wine vinegar for sprinkling
Three 4.5-ounce, 120 g cans tuna in olive oil, drained (or tuna in jars, weighing about 14 ounces/360 g total)
2 beefsteak tomatoes, about 1 pound (450 g total), sliced ¼ inch (0.5 cm) thick
6 to 8 radishes, thinly sliced
2 spring onions, white and pale green parts only, thinly sliced
1 celery stalk, thinly sliced (optional)
2 mild-tasting long green peppers, such as Anaheim, thinly sliced
One 2-ounce, 50 g can anchovies in oil
¼ cup 45 g pitted Niçoise olives
12 large basil leaves
Sea salt and freshly ground black pepper

For the rolls

Turn the dough out on a lightly floured board, gently press out the air, and divide it into 4 or 6 pieces, depending on the size of sandwich that you would like. Shape each one into a ball and place on a baking sheet lined with parchment paper. Flatten the balls to about 1 inch (2.5 cm) thick, using the palm of your hand. Set aside to rise for about 30 minutes.
Preheat the oven to 400°F (200°C).
Make three shallow slashes around the sides of each bun, using a sharp or serrated knife, and bake for about 20 minutes until golden brown. Transfer the buns to a rack to cool completely.

For the eggs, if using

Bring a small pot of water to a boil. Add the eggs to the boiling water and cook for 8 minutes if you like the yolks slightly creamy, or 10 minutes for hard-boiled eggs. Transfer the eggs to a bowl of ice water to cool, then drain, peel, and cut each one into 6 wedges.

Assemble the sandwiches

Split the rolls in half and remove some of the crumb from the top halves, if you like. Gently rub the bottom halves with the cut garlic clove, if using. Drizzle with the olive oil and sprinkle with red wine vinegar to taste.
Place 2 slices of tomato on the bottom half of each bun. Flake the tuna onto them and top with the sliced vegetables. Finish with the eggs, if using, anchovies, olives, and basil and season with salt and pepper. Press the top half of each bun down so that the bread absorbs some of the juices. Let stand for at least 10 minutes, and up to 2 hours, before serving.