1. Using a mandoline (if possible), slice the zucchini and red onion very thinly into 1⁄8-inch
rounds. If you do not have a mandoline, use a sharp knife, and slice as thinly as possible.
2. Transfer to a large bowl, sprinkle with the salt, and toss to coat. Place something heavy,
such as a small cast-iron pan or plate with cans, on top of the zucchini-onion mixture to
promote drainage.
3. After two hours have passed, preheat the oven to 400°F, and line a baking sheet (I use a 13” x 18” baking sheet) with parchment paper, or spray it with oil.
4. Transfer the zucchini and onions to a cheesecloth or thin kitchen cloth, and drain as much liquid as possible into the bowl where the mixture sat. Set the drained zucchini and onions aside. The juice will be used for the liquid base of the scarpaccia.
5. Add the flour, cornmeal, dried rosemary, and nutritional yeast (if using) to the bowl with the zucchini juice. Mix to form a thick batter, similar to a pancake-batter consistency. Add 1/2 to 3/4 cup of additional water, as needed, to thin.
6. Fold in the drained onions and zucchini, and gently mix until evenly dispersed.
7. Pour the batter onto the prepared baking sheet, and, using a spatula, spread the mix evenly, around 1/2 inch thick. For a crispy scarpaccia, spray the top with olive oil.
8. Bake for 35 to 40 minutes, until browned. Remove from the oven.
9. Allow to cool before transferring from the baking sheet and slicing into 12 squares.