Slice and salt. Cut the zucchini into rounds about 1/4 inch (6 mm) thick, lay them in a single layer, sprinkle with the 3/4 teaspoon salt on both sides, and leave for 10 minutes until the surfaces bead with water.
Pat every round dry with a clean towel or paper towels until the surfaces look matte, so the flour clings in a thin, even film.
Set up two stations: flour spread on a small plate, and eggs beaten with a small pinch of salt in a shallow bowl. Coat each round lightly in flour, shake off the excess, then dip in egg and let the extra drip back.
Fry the first side in a thin film of oil over medium heat for 2 to 2 1/2 minutes, until set and golden at the edges. Press a thin chili slice onto a few rounds before flipping, if using.
Flip once and fry 1 1/2 to 2 minutes more, until pale gold and tender. Drain on a rack or paper towels and fry the rest in batches, adding oil and letting the pan reheat between batches.
Stir the soy sauce, rice vinegar, sugar, sesame oil, sesame seeds, and gochugaru together until the sugar dissolves. Serve the fritters hot with the sauce for dipping.