In a small blender, mix the pesto, lemon juice, olive oil, basil, the optional garlic or chilli flakes and salt & pepper. Blitz for a few seconds until you get a coarse paste. Taste and adjust it to your liking.
Transfer the mixture to bowl.
Drain the water from the mozzarella balls then add them to the bowl.
Toss well, until each ball is covered well with the pesto.
Add some more olive oil if you think it’s too dry.
Refrigerate for at least 8 hours before serving.
If you're serving the balls as nibbles or appetizer, remove them from the fridge about an hour before serving, allowing the marinade to come to room temperature.