In a large bowl, whisk the eggs until well blended then mix in the flour, feta, mint, salt and pepper. Mix until well incorporated
Slice the ends off the zucchini. Using the coarse side of a box grater or shredding disk on a food processor, grate the zucchini. Transfer to a clean dish towel and roll up like a burrito. Hold over the sink and twist the ends in opposite directions to squeeze out as much moisture as possible.
Add the zucchini to the bowl, along with the onion and mix to thoroughly combine.
Heat a large sauté pan or griddle over medium heat. When it's hot, add just enough oil to coat the bottom of the pan. Line a large plate or baking sheet with paper towels and set a cooling rack on top.
Working in batches, scoop 2-3 tablespoon dollops of the zucchini mixture on to the hot pan. Use a spatula to flatten each one slightly. Fry until the bottoms turn golden brown, about 3 minutes, turn over onto the other side and fry until the second sides are golden brown, about 2 minutes. Transfer to the wire rack and sprinkle lightly with the flaky salt.
Repeat with remaining zucchini mixture, adding a small amount of oil between batches as needed and letting it heat until it shimmers.
Serve immediately or keep the fritters warm in a 180℉ oven.