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