Cut the potatoes into bite-sized pieces. Put them in a pan of lightly salted water, bring to the boil, then cook for approx. 15 minutes, until tender.
Meanwhile, in a bowl, mix the pesto, garlic, olive oil, lemon zest and juice. Add the mozzarella balls, toss well and set aside.
When the potatoes are cooked, drain and put them in a serving bowl.
Add the mozzarella mixture, including the marinade and toss gently. Season to taste.
Cover with a plate or lid and rest for 5 minutes until the cheese melts over the potato pieces.
Serve warm with chopped parsley leaves.