1. Salt the Vegetables: Place the thinly sliced zucchini and onion in a large bowl. Add 1 teaspoon of salt and toss the mixture with your hands. Transfer the mixture to a colander set over a bowl and let it sit for at least an hour.

2. Preheat Oven: Preheat your oven to 425 degrees F. Line a 9×13-inch metal baking dish with parchment paper and brush it with olive oil. Sprinkle cornmeal on top.

3. Make the Batter: In a large bowl, combine the flour, cornmeal, grated Parmesan cheese, garlic powder, smoked paprika, dried oregano, remaining salt, and black pepper. Slowly pour in the reserved zucchini liquid, adding water as necessary to achieve a consistency of 1 1/4 cup. Add 2 tablespoon of olive oil and whisk until smooth.

4. Combine: Gently fold the drained zucchini and onion into the batter until evenly coated.

5. Spread and Top: Transfer the batter and vegetable mix into the prepared baking dish and spread it out evenly. Drizzle the remaining olive oil over the top and sprinkle with extra cornmeal, more Parmesan, and chopped fresh rosemary.

6. Bake: Bake for about 45 to 50 minutes until golden brown and crisp. Invert onto a cooling rack for an additional 10 minutes for extra crunch.