Pan Bagnat is the ultimate tuna fish sandwich. This layered sandwich from the South of France, meaning "bathed bread," is stuffed with tuna, vegetables and oil-cured olives, and drizzled with a lemon dressing. The sandwich is then pressed, marrying the tuna and vegetables, thus bathing the bread in flavor. This sandwich is sure to steal the show at any picnic.
In a small bowl, gently flake tuna and mix with herbs and set aside.
In another bowl, whisk lemon juice, mustard, salt and pepper. Slowly drizzle in olive oil until emulsified. Set aside.
To assemble sandwich, cut bread lengthwise and hollow out loaf of bread (save the insides for breadcrumbs). Place fennel in an even layer over the bottom of the bread and then top with cucumbers, red bell pepper and tomatoes. Spread with tuna mixture and then continue to layer eggs, olives and anchovies. Drizzle reserved lemon dressing evenly over sandwich and season with salt and pepper. Cover with top of bread and wrap the sandwich in a couple layers of plastic wrap or tin foil.
Place in between two baking sheets, weighing down the top sheet with something heavy, such as a cast iron skillet, a brick or large cans of tomatoes. Refrigerate for 3 hours to 8 hours. Remove from refrigerator, unwrap and slice into wedges. Serve cold or at room temperature.