Trim ends off zucchini and grate them on the large holes of a box grater over a large bowl.
Wrap zucchini in a clean kitchen towel and place in a colander to drain for at least 10 minutes.
Wring out the zucchini by pressing it against the holes of a colander to extract the water.
Return zucchini shreds to bowl. Stir in scallions, egg and some freshly ground black pepper.
In a tiny dish, stir together flour and baking powder, then stir the mixture into the zucchini batter. It should look like lightly coated zucchini- this is not a runny batter.
In a large non-stick skillet, heat 1 teaspoon oil over medium-high heat. Drop four small bunches of the zucchini mixture (about a quarter cup) onto the skillet. Do not overcrowd them.
Cook the fritters over moderately high heat until the edges underneath are golden, about 3 to 4 minutes. If you find this happening too quickly, reduce the heat to medium. Flip the fritters and fry them on the other side until browned underneath again, about 2 to 3 minutes more.
Repeat process with remaining batter.
For the sauce, stir together the yogurt, salt, and mayonnaise and adjust the flavors to your taste. Use a mortar and pestle to grind the garlic into a fine paste before adding it to the yogurt. Dollop on each fritter before serving and sprinkle with sumac.
Tip
These fritters keep well, either in the fridge or frozen. When you need them, reheat them in your toaster oven until they’re hot and crisp again.
Recipe by Kiku Corner at https://www.kikucorner.com/2014/02/28/fresh-and-light-zucchini-fritters/