MIX DOUGH
In a stand mixer with the dough hook, mix the flour, yeast and sugar on medium until combined, about 30 seconds.
With the mixer on low, drizzle in the water, then increase to medium and mix until the ingredients form a very wet, smooth dough, about 5 minutes.
Turn off the mixer, cover the bowl and let stand for 10 minutes. Meanwhile, coat the bottom and sides of a large bowl with 2 tablespoons of oil; set aside.
REST DOUGH
Sprinkle 2 teaspoons of salt over the dough, then knead on medium until smooth and elastic, about 5 minutes; the dough will be wet enough to cling to the sides of the bowl.
Using a silicone spatula, scrape the dough into the oiled bowl. Dip your fingers into the oil pooled at the sides of the bowl and dab the surface of the dough until completely coated with oil.
Cover loosely with plastic wrap and let stand at room temperature for 5½ to 6 hours; during this time, the dough will double in volume, deflate, then rise again (but will not double in volume again).
PREPARE OVEN
After the dough has risen for about 4½ hours, heat the oven to 500°F with a baking steel or stone on the middle rack.
Mist a 9-by-13-inch metal baking pan with cooking spray, then pour the remaining 2 tablespoons oil in the center of the pan; set aside.
PREPARE PAN
When the dough is ready, gently pour it into the prepared pan, scraping the sides of the bowl with a silicone spatula to loosen; try to retain as much air in the dough as possible.
The dough will eventually settle into an even layer in the pan; do not spread the dough with a spatula, as this will cause it to deflate. Set aside while you prepare the tomatoes.
ADD MOZZARELLA, SALAMI, TOMATOES AND OLIVES
Scatter the mozzarella on the dough. In a medium bowl, use a potato masher to lightly crush the tomatoes. Scatter the olives evenly over the dough, then do the same with the tomatoes, leaving the juice and seeds in the bowl. Scatter the desired amount of salami slices.
If the dough has not fully filled the corners of the pan, use your hands to lightly press the tomatoes to push the dough into the corners. Let stand uncovered at room temperature for 20 minutes.
BAKE AND SERVE
Drizzle the dough with ¼ cup oil, making sure to oil each tomato. Sprinkle evenly with oregano, the remaining 1½ teaspoons salt and ¾ teaspoon pepper.
Place the pan on the baking steel or stone and bake until golden brown and the sides have pulled away from the pan, 20 to 22 minutes. Cool on a wire rack for 5 minutes.
Using a wide metal spatula, lift the focaccia from the pan and slide it onto the rack. Cool for at least 30 minutes before serving.
