Place each tomato with the stem side down and make six slices to within 1/2 inch from the base, taking care not to cut all the way through.
Cut the fresh mozzarella into 12 thin slices. Chop the black olives into small dice.
Place a piece of mozzarella in between each tomato slice.
In a bowl, combine the vinegar and olive oil and season with salt and pepper. Drizzle over the tomatoes and sprinkle with chopped olives.
Serve on some lettuce leaves or arugula.