In a large bowl, combine dry ingredients of dough, stirring to distribute. Create a well in the flour mixture and add warm water (no more than 115F) and oil. Stir vigorously until a sticky dough forms and all flour is incorporated.
Turn dough out on a lightly floured surface. Knead by stretching and folding the dough back on itself. Continue for about 5 minutes of 60 turns. The dough should become smoother and fully pull away from the surface, easily forming a ball. Alternatively, you can process the dough in a stand mixer with a dough hook for 5-6 minutes.
Oil a large bowl. Roll the dough in the bowl so that it is covered in oil. Cover with a damp cloth or cling wrap. Allow the dough to rise at room temperature until 2.5 or 3 times the size, about 1.5 to 2 hours depending on the ambient temperature.
Line a baking sheet with parchment paper.
Turn risen dough out on a parchment paper. Stretch with your fingers to approximately 9"x14" rectangle. Cover with a damp cloth or cling wrap and allow to rest for 15-20 minutes.
Slice lemon into extremely thin rounds, less than 1/8 inch. You can use a mandoline or a very sharp knife.
Preheat the oven to 425F.
Uncover the dough. Use your finger to push dimples into the dough about 2" apart.
Top with thinly sliced lemon, sprinkle with rosemary and flaky salt.
Bake for 12 minutes at 425F. Reduce the heat to 400F and bake for another 9-10 minutes until the top begins to brown. Remove from oven and allow to cool for at least 20 minutes.