Add bread flour, Kosher salt, and instant yeast to a large mixing bowl and stir briefly to combine. Add the olive oil and water and stir with a wooden (or similar) spoon. The dough will slowly begin to come together in scraggly scraps. If there is too much unincorporated flour in the bottom of the bowl, add more warm water, one tablespoon at a time, until combined. Note that you don't want the dough to become too wet - it's better to leave a little flour behind than have soggy dough.

Turn out the dough onto a lightly floured surface, and knead for about five minutes, or until the dough becomes soft and pliable and forms a smooth ball.

Place in an oil-rubbed bowl, with room enough to expand, cover, and let rest for one hour or until doubled. If making ahead, you can place the bowl in the refrigerator. The dough will rise slowly in the cold temps, but will keep for a couple of days.

Heat the grill or a stovetop grill pan on medium-high.

Turn out the dough onto a roomy surface and pat into a rectangle. Use a sharp knife or bench cutter to divide the dough into 4 or 6 pieces (4 will create a nice size for soup; 6 as a side for a more substantial meal).

Flatten one dough ball, and then roll out to a thickness of about 1/4". The shape can be irregular. Repeat with the remaining pieces.

Lightly brush one side of the first flatbread with olive oil, sprinkle with finishing salt, place oiled side down on the hot grill. Lightly brush the "up" side with olive oil and sprinkle with more salt. When the flat bread is puffy and bubbly (just a few minutes), flip (it should be sturdy). Sprinkle the grilled side with za'atar. When the underside is done, remove from the heat and repeat with the remaining flatbreads (if your grill has room, you can cook them all at the same time).

You can serve the hot flatbreads immediately, or leave them to sit at room temp for an hour or so.