Slice and salt zucchini – Use a mandoline or sharp knife to cut zucchini paper-thin. Toss with 1 tsp salt and let rest for 30 minutes. Pat dry.
Make batter – In a large bowl, whisk flour, cornmeal, water, salt, and pepper until smooth. Batter should be thin like crepe batter.
Combine – Add zucchini, onion, olive oil, and herbs to batter. Mix gently.
Prepare pan – Grease a large baking pan generously with olive oil.
Spread thin – Pour mixture into pan and spread into an even, thin layer.
Bake – Bake at 400°F (200°C) for 35–45 minutes, until deep golden at edges. Rotate pan halfway.
Cool & serve – Let rest for 10 minutes before slicing. Serve warm, room temp, or chilled.