Essentially a Niçoise salad in sandwich form, the pan bagnat is sold at nearly every outdoor market in Nice, France, as well as at bakeries and restaurants. For this version, tuna is pureed with red wine vinegar, olive oil, anchovies, and garlic to form a unique sandwich spread inspired by tonnato sauce. Spreading a tangy tuna dressing on the cut sides of the ciabatta allows it to get absorbed into the bread, giving the sandwich plenty of flavor while also making it easier to eat.