1. Wash the tomatoes well. Cut crosswise to make 1/4-inch slices. Cut the fresh mozzarella cheese to make 1/4-inch slices. Wash the basil leaves.
2. In a small bowl, mix vinegar, olive oil, and dried oregano. Season with salt and pepper to taste.
3. On serving plates, arrange tomato slices and black olives. Top with sliced mozzarella cheese, and sprinkle dressing over the salad. Garnish with basil leaves.