Pan Bagnat with Fennel Recipe

Ingredients

• 1/2 fennel bulb, very thinly sliced
• 1/2 cup mixed pitted olives, chopped
• 1/4 cup olive oil
• 3 tablespoons white wine vinegar
• 2 tablespoons chopped drained capers
• 1/2 teaspoon crushed red pepper flakes
• Kosher salt, freshly ground pepper
• 1 Persian or 1/4 English hothouse cucumber, thinly sliced
• 2 (6-7-ounce) cans olive oil–packed tuna, drained
• 1 12"-long ciabatta loaf, halved lengthwise
• 3 hard-boiled large eggs, peeled, sliced
• 2 cups arugula