In a food processor, or using a stick blender, blend the chickpeas, yoghurt, olive oil, harissa paste, lemon juice and salt & pepper until you've got a texture you like. I like mine super smooth - but others like theirs with more texture. You decide. Add some of the chickpea liquid if it's too thick.
Arrange in a bowl and pour over more extra virgin olive oil and scatter generously with the za'atar.
I usually serve this as a communal offering, so will serve with lots of warmed flatbreads. I will sometimes serve as an accompaniment to meat and poultry too.