Slice zucchini and half of a red onion into thin slices. Place into a large mixing bowl and toss with two teaspoons of salt.
Cover the bowl and place in the refrigerator for a minimum of 30 minutes and up to 1 hour. This will push out excess water.
Preheat the oven for 400° F.
In a medium sized mixing bowl, mix flour, cornmeal, dry basil, pepper, and parmesan cheese.
Remove the zucchini and onion from the refrigerator. After 30 minutes, they have let go of a lot of the water and will be very damp. (The moisture is the liquid for our batter. Some recipes have you squeeze out all of the liquid and mix it with the dry ingredients to form a batter. We are going to leave it right in the same bowl and add the dry mixture to zucchini, onions, and all of their liquids.
Add the dry ingredients to the bowl of sliced zucchini and mix until a batter forms around the vegetables.
Place the scarpaccia batter on a sheet pan lined with parchment or well greased. Spread the batter evenly into a thin layer and press the layer flat with the palm of your hand.
Drizzle the olive oil over the top and sprinkle the remaining half of a cup of parmesan evenly over the top.
Bake for 35-45 minutes, until the top is brown and crisp.
Remove from the oven and let sit on the baking sheet for 30 minutes. Then, cut into 12 even pieces and serve slightly warm to room temperature.