Whisk together the sourdough starter and water in the bowl of your stand mixer. Measure in the flour and salt, and stir to combine at low speed.
Once combined, knead on medium speed (4-6) for about 10 minutes or until the dough no longer sticks to the sides of the bowl and climbs the hook.
Use 1 Tablespoon of oil to lubricate your work surface, and turn the dough out onto the oiled surface. Then, drizzle an additional 1 Tablespoon on top. Knead with your hands for 5 minutes until the oil is worked in, or until the dough starts to stick to the counter.
Form a ball, and move to a large bowl coated with 1 Tablespoon of oil. Cover with airtight lid, and proof for 4 to 6 hours or until doubled in size.
Add 2 Tablespoons of oil to a 9x13 pan and rub it into the bottom and sides. Turn the dough out into the pan and stretch it to fit the bottom.
If dough resists stretching, let it rest for 5 minutes before trying again. Repeat until your dough has stretched to fit the pan. Cover and proof again for 2 hours or until visible bubbles form.
Preheat the oven to 425ºF.
Halve your tomatoes and chop the herbs, as desired. Use as much as you want, the measurements above are loose recommendations.
Drizzle 2 Tablespoons of oil on top of the loaf, and rub it over the surface with your hands until your hands and the focaccia are well-coated. Use your fingers to press dimples into the surface of the bread.
Stud the dimples with halved tomatoes, with the cut side facing up. Sprinkle the herbs or create a design as you wish. Finally, sprinkle the top of the loaf evenly with a healthy pinch or two of salt, to your preference.
Bake for 25 minutes. Allow the bread to cool in the pan until it's comfortable to touch. Then, remove it to a wire rack to finish cooling completely before serving.