Preheat oven to 425°F (220°C) and line a 9×13-inch baking dish with parchment paper. Lightly grease it with olive oil.
Toss sliced zucchini with 1 teaspoon salt in a bowl. Let it sit for 15–20 minutes to release moisture. Use a clean towel to squeeze out excess water.
In a large mixing bowl, combine cornmeal, flour, parmesan, garlic powder, oregano, and black pepper.
Add eggs and olive oil to the dry mixture and stir until a crumbly batter forms.
Fold in the drained zucchini and sliced onions until evenly coated.
Spread the mixture evenly into the prepared baking pan and press down gently.
Bake for 40–45 minutes, or until golden and crispy on the edges.
Cool for 5–10 minutes, then slice into squares. Serve warm, optionally garnished with basil and lemon wedges.