Preheat the oven to 425℉ and line a small baking sheet with parchment paper.
Cut the tomatoes into ¼'' thick slices and lightly sprinkle over some of the salt. Let them sit for a few minutes, then pat them dry and set aside.
Lightly dust a work surface with flour and roll the puff pastry into a rectangle until very thin, about ½ centimeter. Place the dough onto the prepared baking sheet.
Evenly spread the Dijon mustard onto the surface of the pastry, leaving at least a ¾ inch border along the edges. Stir together the tomato paste and tomato sauce, then spoon the mixture over the mustard layer. Sprinkle over the breadcrumbs.
Layer the sliced tomatoes over the breadcrumbs in three rows until the pastry is covered. Generously sprinkle the salt and pepper over the tomatoes, then fold the puff pastry border over the tomatoes to encase them.
Drizzle over the olive oil and herbes de Provence. Bake the tart for 35 minutes, until the pastry is golden-brown and fully cooked. Sprinkle over the cheese, slice, and serve warm!