Grate the zucchini on the large holes of a grater onto a clean kitchen towel. Sprinkle with the kosher salt and let it rest while you gather and prep the remaining ingredients.
Wrap the zucchini in the towel and ring as much liquid out as possible, discarding the liquid. In a medium bowl, combine the zucchini, mint, dill, scallion, garlic, pepper, feta, and all but 1 teaspoon of the lemon zest. Stir in the egg and flour and mix until well combined.
Add the canola oil to a large shallow pan; you want about a inch or enough so that when all the fritters are in the pan, the oil comes halfway up their sides. Place the pan over medium-high heat. Form fritters by hand or by using cup measure, and fry them in the hot oil in batches. Cook until the fritters are golden brown on each side, 4-6 minutes. Drain on paper towels.
Transfer the fritters to plates and garnish with a dollop of Greek yogurt and a sprinkling of dill, the reserved lemon zest, and some course sea salt.