Prepare the Onions: Slice the red and yellow onions into thin rings, and soak them in cold water for 5-10 minutes. Drain well afterward.
Make the Dough Base: In a large bowl, whisk together the water, flour, olive oil, and salt until the mixture is smooth and forms a fairly liquid batter.
Add the Onions: Stir in the drained onions into the batter until they are evenly coated.
Prepare the Baking Tray: Line a rectangular baking tray with parchment paper, drizzle with olive oil, and pour the batter into the tray, spreading it out evenly.
Top with Cheese and Cornmeal: Sprinkle the grated vegan parmesan evenly over the onions, followed by a light dusting of the cornmeal.
Final Touch: Drizzle a little olive oil on top to give extra flavor and crispness.
Bake: Preheat your fan oven to 392°F (200°C). Bake the Schiacciata for 30-40 minutes or until golden and crispy on the edges.
Serve: Once baked, take it out of the oven, let it cool for a few minutes, and serve warm.
