In base of a stand mixer fit with dough attachment, stir together warm water, yeast, sugar, flour, salt, olive oil, and Italian seasoning until a ball of dough forms. If the dough is too wet, sprinkle in flour, about 1/2 tbsp at a time. And if the dough is too dry, add a splash or two of water.
Spray a bowl with baking spray and place dough ball in bowl. Turn dough so that all sides become covered in spray from being rolled in bowl. Cover bowl with a dish towel and let rise in a draft free area for about 1 hour.
After dough has risen for an hour, preheat oven to 450 degrees.
Punch down dough and divide in half. If not making two pizzas, you can wrap the second half in plastic wrap and freeze.
Stretch one half of dough to evenly cover the inside of a 12" cast iron skillet.
Spread pesto over dough. Place tomato slices on top of pesto. Sprinkle each slice of tomato with a pinch of kosher salt. Then, place mozzarella evenly over top of pizza.
Bake for 15-20 minutes, or until cheese is melted and the crust has risen and has started to brown. I recommend that you cook the pizza on the top rack of your oven. Time will vary depending on type of oven and placement in oven.
Remove skillet from oven. Divide Prosciutto evenly over the top of the pizza, followed by the arugula. Drizzle balsamic reduction over the top of entire pizza.