Whisk yogurt, lemon juice, and sugar in a small bowl to combine. Season with salt and whisk again to combine.

Do Ahead: Yogurt can be made 1 day ahead. Cover and chill.

Rinse lentils, then soak in 2 cups water at room temperature at least 1 hour and up to 12.

Meanwhile, trim ends of zucchini and cut crosswise into 3 pieces about 2" long. Cut each piece lengthwise into ¼"-thick planks. Stack a few planks and slice lengthwise into ¼"-thick matchsticks.

Transfer zucchini to a colander set in a medium bowl. Add onion and 1 tsp. salt to colander and toss to combine. Let zucchini and onion sit until about 1 Tbsp. liquid has released and the vegetables look wilted and soft, 30 minutes–2 hours.

Gently pat dry with paper towels to remove any excess moisture.

Drain lentils and transfer to a food processor. Add chile powder, turmeric, and ¾ tsp. salt. Pulse, scraping down sides, until a purée forms.

Transfer to a medium bowl and add zucchini and onion mixture, parsley, and lemon zest. Toss well with a rubber spatula to combine.

Heat ghee in a 10" cast-iron skillet over medium-high until a small amount of batter added to the fat excitedly sizzles and sputters.

Carefully drop ¼ cup batter into ghee, then flatten to a pancake with the back of a large metal spoon dipped into the hot ghee to prevent sticking. Repeat 3 times for a total of 4 fritters.

Fry until deep golden brown on one side, about 3 minutes. Turn and continue to fry until deep golden brown on the second side, about 3 minutes more.

Transfer fritters to a wire rack set in a paper towel-lined baking sheet to drain. Season immediately with salt. Repeat with remaining batter.

Transfer fritters to a platter. Serve hot with lemony yogurt alongside.