Pour off the mozzarella balls, drain and transfer to a sealable can or bowl. Add the pesto, oil, salt and pepper. Press the fresh garlic over it. Close the can and shake well so that all the balls are covered with the marinade. Let it steep in the refrigerator for at least 2 hours, even better overnight. Shake it twice more in between.
After marinating, stick the balls with a tomato and a fresh basil leaf on a toothpick or small skewer and arrange on a plate or tray and serve.