Put warm water and yeast together in a bowl. Let it sit for 5 minutes or until the yeast has activated. Add in the sugar, salt, olive oil, cornmeal, flour, baking powder, garlic powder, and onion powder. In your stand mixer, mix them with the paddle attachment just until combined. Then put on the dough hook and knead for about 10 minutes. Cover with plastic wrap and let rise in a warm place for 30 minutes or until doubled.
Preheat the oven to 550 degrees. Divide the pizza dough into 6 balls. Dough should be a bit sticky. Press each ball out into a circle. Place 5 pepperoni slices on half of the circle. Then put about 1/3 to 1/2 cup shredded mozzarella cheese over the pepperoni. Place another 5 pepperoni slices on top of the cheese. Fold the circle in half. Turn the edges in and press to seal the calzone.
Brush the tops of the calzones with olive oil and sprinkle with garlic salt. Put a bit of shredded mozzarella on top, if desired. Place the calzones on a baking sheet.
Bake the calzones at 550 degrees for 8 minutes or until golden brown.
*If you'd like, you can use your breadmaker on the dough setting to make this dough. *If your oven doesn't go up to 550 degrees, set it to as high as it will go. You will need to add a few minutes to the baking time.