Slice each mozzarella ball into 4 even rounds. Set aside. Do the same with each tomato.
Assemble each dish starting with a slice of tomato and then top with a slice of mozzarella. Repeat once and then finish off with a slice of tomato. When you are assembling the dish, smear some of the pesto in between the layers.
Finish off with a drizzle of olive oil and a scattering of fresh basil leaves.