Arrange 4 tomato slices and 2 mozzarella slices on each of 6 salad plates. Sprinkle evenly with salt and pepper; drizzle with oil. Top evenly with basil.
In Italy, this is known as insalata caprese (Capri-style salad). It's best in summer, when tomatoes are at their peak. If you can get imported Buffalo mozzarella from Italy, use it, but domestic fresh mozzarella is fine, as well. Fresh mozzarella cheese is packed in water. It has a softer texture and sweeter, more delicate flavor than the regular part-skim mozzarella that is more commonly used in cooking for its superior melting qualities.