Author Notes: The pan bagnat is the sandwich version of the salad Nicoise.
You can find either in various forms all over the Mediterranean coast where it is made with fresh seasonal ingredients. Here, olive oil packed canned tuna is mixed with olives, red onions, fresh herbs, and vinaigrette. The salad fills the center of a crusty French baguette. In this case "crusty" is the operative word. The bread must have a hard crust on the outside otherwise it will fall apart. Pan Bagnat literally translated is "wet bread" - the point is for the vinaigrette to soak into the bread. In my opinion, THAT is what makes this such a great sandwich.

Pan Bagnat: Le French Tuna Salad Sandwich

Serves: 2, but multiplies easily 
Prep time: 8 hrs 10 min

• 1/2loaf crusty French baguette
• 1clove garlic, cut in half
• 4to 6 basil leaves
• 1(6oz) can tuna
• 3/4cup Nicoise or Kalamata olives, sliced
• 1/2cup red bell pepper, seeded and sliced thin
• 1/2small red onion, finely chopped
• 1/4cup Italian flat leaf parsley, finely chopped
• 1jar or can artichoke hearts, drained and chopped (optional)
• 1/4cup blanched French green beans, sliced into thirds (optional)
• 3tablespoons fresh lemon juice
• 6tablespoons extra virgin olive oil, plus more for drizzling
• 1pinch sea salt and freshly ground black pepper, to taste

1. PREP THE BREAD: Slice the loaf of bread in half lengthwise. Remove some of the insides of the bottom half to create a trough into which the filling will go. Brush both halves with a little extra virgin olive oil. Rub each with the garlic. Line the half with the trough with the basil leaves.
2. MIX THE SALAD: In a mixing bowl, combine the tuna, olives, red bell pepper, onion, parsley, artichoke hearts (if using) and green beans (if using). In a measuring cup or small bowl, whisk the lemon juice into the olive oil until it is emulsified/combined. Pour the vinaigrette into the tuna mixture and stir to combine. Season to taste with sea salt and pepper.
3. ASSEMBLE: Spoon tuna mixture into the trough of the baguette over the basil leaves. Wrap sandwich well in plastic. Crush it down by placing a brick or heavy cast iron skillet and refrigerate, preferably with the weight, overnight.
4. SERVE: In the morning, cut sandwich in half. Enjoy for lunch at home or wrap in foil and brown bag it (use a lunch box that will keep the sandwich chilled). Serve with cubes of feta cheese and a tart Granny Smith apple.

https://food52.com/recipes/6896-pan-bagnat-le-french-tuna-salad-sandwich