Wash the tomatoes. Remove the stalk and cut the tomatoes into slices. Drain the mozzarella and cut into thin slices. Arrange the tomato and mozzarella slices on a plate.
Whisk together the oil and balsamic vinegar. Finely chop the basil and mix in. Drizzle the dressing over the tomatoes and mozzarella. Let stand in the refrigerator for a few hours until ready to eat.