Cook the balsamic vinegar in a small saucepan over low heat until thick, syrupy, and measuring 1/4 cup, about 20 minutes. Set aside to cool.
Combine the olives, parsley, anchovies, capers, garlic, basil, pepper, and olive oil in a small bowl and toss to combine.
To serve, slice the tomatoes into 1/4-inch thick rounds and place, slightly overlapping, on a serving plate. Spoon the olive and parsley mixture over the tomatoes. Drizzle the reduced balsamic over the salad and serve.