Preheat oven to 250C. Wrap each buffalo mozzarella with a prosciutto slice, secure with a toothpick and place on an oven tray lined with baking paper. Drizzle with oil and roast until mozzarella just begins to melt (4-5 minutes).
Meanwhile, heat a char-grill over medium-high heat, grill ciabatta slices until golden (3-4 minutes each side).
For Dijon mustard dressing, whisk mustard and lemon juice in a bowl to combine, then whisk in oil and sugar, season to taste and set aside.
Place a grilled ciabatta slice on each plate, top with a baked mozzarella, season with freshly ground black pepper. Combine herbs in a separate bowl. Serve mozzarella warm with herbs to the side and dressing drizzled over.