Here, za'atar is the term for the Middle Eastern spice mix made from a heady combination of herbs, spices and seeds; however, it's also the name of a herb itself. As with so much Middle Eastern cooking, there are many regional variations.
Heat oven to 110C/90C fan/gas 1/4. Put the pittas on top of each other on a chopping board. With a bread knife, cut them into quarters, then cut each quarter in half again (so you end up with 16 equal-sized triangles).
Add the olive oil, a pinch of salt and the za’atar to a small bowl, and stir to combine. Using a pastry brush or your finger, coat the pittas on both sides with the mixture, then put them on a baking tray and bake in the oven for 30-40 mins until crisp.