Combine water and yeast in a large bowl. Add 1 cup flour and 1/2 tablespoon salt. Stir using a wooden spoon until combined. Stir in olives, reserved herbs and garlic, and garlic powder until incorporated. Add remaining flour 1 cup at a time, stirring until thoroughly combined. Cover the bowl with plastic wrap and set in a warm spot until dough has doubled in size, about 1 hour.

Add 1 tablespoon olive oil to an 8-inch cast iron skillet and spread to coat the bottom and sides. Flour your hands. Remove plastic wrap from the bowl, transfer dough to the prepared skillet, and shape into a disc. Cover with a kitchen towel and let stand for 30 minutes.

Preheat the oven to 400 degrees F (200 degrees C).

Drizzle remaining 1 tablespoons olive oil on top of the loaf and sprinkle with coarse salt and parsley. Score the top of the loaf about 1/2-inch deep with a sharp knife.

Bake in the preheated oven until the top is nicely browned, 30 to 35 minutes. Remove bread from the oven and turn out onto a wire rack to cool before serving, about 20 minutes.