To make the lebneh, place a few sheets of cheese cloth or paper towels in a fine mesh sieve. Place the sieve over a bowl and put the yogurt into the sieve. Allow to drain for at least 8 hours in the refrigerator. Salt and pepper to taste.
Preheat your oven to 400F. If you have a pizza stone, allow to heat up with the oven.
Place all ingredients in the bowl of a stand mixer. Mix on medium low with the dough hook attachment for about 10 minutes. You want to build good gluten structure. You know the dough is ready when you can stretch a piece and it's translucent and doesn't tear. Something similar to pizza dough.
Let dough rest for 10 minutes.
Roll out in desired sizes on parchment. Either place directly onto a pizza stone or bake on a metal sheet tray.
Bake flatbread for about 10-12 minutes - shorter times yields a chewier softer crust, long times will yield a crunchier and crispy bread.
After the bread has cooled slightly, spread a few tablespoons of the lebneh onto the flatbreads.
Drizzle with a little extra olive oil and za'tar spice if desired. Serve warm.