Sandwiches - Pan Bagnat

Pan Bagnat is basically Salade Nicoise on a bun.
1 T red wine vinegar
1/2 t dijon mustard
1/2 t kosher salt
1/4 t pepper
3 T olive oil
4 large round rolls
12 oz tuna
1/4 cup chopped green pepper
1/4 cup chopped red onion
2 hardboiled eggs, sliced
1 cup chopped Nicoise or similar pitted olives
1 tomato, sliced

In a small bowl, make a vinegarette by whisking vinegar through pepper. Gradually add oil, whisking. Slice rolls; tear out some center to form a well. Mix tuna through olives with some dressing. Stuff rolls. Serve with sliced eggs and tomatoes. Serves 4.