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
• Kosher salt, freshly ground pepper
• 1 12"-long ciabatta loaf, halved lengthwise
• 3 hard-boiled large eggs, peeled, sliced
• 2 cups arugula

Instructions

1. Toss fennel, olives, oil, vinegar, capers, and red pepper flakes in an airtight container or resealable plastic bag; season with salt and pepper.
2. Do Ahead Fennel-olive mixture can be made 2 days ahead. Cover and chill.
3. Fennel-olive mixture can be made 2 days ahead. Cover and chill.
4. Assembly: Toss fennel-olive mixture with cucumber and tuna in a medium bowl; season with salt and pepper. Let sit, tossing occasionally, 10 minutes. Scoop out inside from top half of bread; discard (or save for a snack!). Layer bottom half of bread with tuna mixture, then top with eggs and arugula. Close up sandwich. Place a large heavy skillet or pot on top of sandwich to weigh down and let sit at room temperature, turning once, until evenly pressed, about 2 hours (if making sandwich at home, or storing in a cooler while you hike, wrap it up tightly in plastic wrap before you press it). Slice pan bagnat into wedges just before serving.
5. Toss fennel-olive mixture with cucumber and tuna in a medium bowl; season with salt and pepper. Let sit, tossing occasionally, 10 minutes.
6. Scoop out inside from top half of bread; discard (or save for a snack!). Layer bottom half of bread with tuna mixture, then top with eggs and arugula. Close up sandwich.
7. Place a large heavy skillet or pot on top of sandwich to weigh down and let sit at room temperature, turning once, until evenly pressed, about 2 hours (if making sandwich at home, or storing in a cooler while you hike, wrap it up tightly in plastic wrap before you press it).
8. Slice pan bagnat into wedges just before serving.