Using a mandoline or sharp knife, cut the zucchini into approximately ⅛-inch-thick rounds.
Place the zucchini slices in a bowl of cold water and soak for 15 minutes. Transfer to a colander and drain thoroughly.
In a shallow bowl, whisk together the flour, fine cornmeal, cornstarch, ½ teaspoon sea salt, and black pepper.
Pour 2–3 inches of vegetable or sunflower oil into a heavy-bottomed pot and heat to 365°F.
Working in batches, lightly coat the zucchini slices in the flour mixture, shaking off any excess.
Carefully add the zucchini to the hot oil in small batches. Fry until crisp and lightly golden, flipping as needed. Transfer with a spider strainer or slotted spoon to a paper towel-lined plate or wire rack.
Season the hot zucchini chips with additional sea salt to taste and finish with freshly grated Kefalotyri or parmesan (optional). Serve immediately with tzatziki.