In the bowl of a stand mixer, dissolve yeast in 1 3/4 cups warm water (90° to 105°). Let sit until foamy, about 5 minutes.
Attach dough hook and, with mixer on low, add olive oil, flour, and 4 tsp. salt. Mix until dough is smooth, about 2 minutes. (It will still be fairly sticky and won't pull away from the inside of bowl.) Using a spatula or oiled hands, put dough in a large, oiled bowl, cover with a clean towel or plastic wrap, and let sit until doubled in bulk, 1 1/2 to 2 hours.
Meanwhile, slice lemons as thinly as possible. Discard any seeds. Put lemons and 1 tbsp. salt in a bowl. Let sit at room temperature at least 1 hour and up to 1 day.
Preheat oven to 425°. Lightly oil two 10- by 15-in. baking sheets. Punch down dough, divide in half, and put each half on a baking sheet. Flatten dough as much as possible, pushing gently from the center out. (Dough will pull back toward the center; don't worry if it doesn't stay in place.) Let rest 10 minutes and then flatten again, pushing the edges and corners down to help them stay put (if it pulls back a bit, that's okay, but you want to make the dough as thin and flat as possible).
Lift lemon slices out of their juices and lay them evenly over the dough, pressing them into dough as much as possible. Sprinkle dough with remaining 2 tsp. salt. Bake until brown and crispy, about 25 minutes. While bread is still warm, cut each sheet into 15 pieces. Cool on wire racks.