In a bowl, mix together the yogurt, half a tablespoon of oil, the garlic and herbs. Add the chicken fillets, cover and leave to marinate for a couple of hours or overnight.
Preheat the grill. Place the chicken and its marinade into a foil-lined grill pan. Cook for about 8 minutes until cooked through, with no pink showing, then wrap in the foil and leave to rest for a couple of minutes.
Meanwhile, boil the potatoes until tender, drain, smash roughly with a fork and stir in the remaining olive oil and the zest. Season to taste and garnish with some parsley leaves.
Serve the chicken with the potatoes and some salad.
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