Preheat oven to 400°F (205°C).

Wash and dry the zucchini, then slice very thin using a sharp knife or mandoline.

Place zucchini in a bowl, sprinkle with salt, toss gently, and let sit for 15–20 minutes.

Squeeze out as much liquid as possible using your hands or a clean kitchen towel.

In a large bowl, whisk together flour, water, olive oil, and black pepper until smooth and thin.

Add the drained zucchini and sliced onion to the batter and mix until evenly coated.

Generously oil a baking sheet or shallow pan.

Spread the zucchini mixture evenly and very thinly across the pan, pressing it down gently.

Sprinkle Parmesan cheese evenly over the top and add herbs if using.

Bake for 35–40 minutes until the edges are crisp and golden.

Let rest for 5 minutes before slicing and serving.