In a large bowl, combine the sliced zucchini and red onion. Sprinkle with 1 tsp of salt and gently massage the mixture with your hands. Let it sit for 10–15 minutes to draw out moisture.
Using your hands, squeeze the zucchini-onion mix over a sieve or colander, collecting the liquid in a bowl beneath. Set the veggies aside and keep the liquid.
In the bowl with the reserved liquid, add the flour, cornmeal, and enough water to form a smooth, pourable batter—like pancake batter. Mix until well combined, then fold in the drained zucchini and onion mixture.
Preheat your oven to 200°C (390°F). Grease a baking tray generously with olive oil, then dust it with cornmeal.
Pour the batter into the tray and spread it evenly. Drizzle more olive oil on top and sprinkle with a touch more cornmeal for crispiness. Bake for 35–45 minutes, or until golden brown and crisp on the edges.
Let it cool slightly, then top with fresh basil leaves. Serve warm or at room temperature.
