Whisk together the yogurt, lemon juice, and sugar in a small bowl. Season with a pinch of salt, whisk again, and set aside. This can be made a day ahead and chilled.

Rinse the lentils and soak them in 2 cups of water at room temperature for at least 1 hour, up to 12 hours. The longer soak makes them plump and tender for easy blending.

Trim the ends of the zucchini and cut into 3 pieces about 2 inches long. Slice each piece into ¼-inch planks, then cut lengthwise into ¼-inch matchsticks. Place zucchini in a colander set over a bowl. Add sliced onion and 1 teaspoon salt, toss to combine, and let sit until the vegetables release about 1 tablespoon of liquid and look wilted, 30 minutes to 2 hours. Pat dry with paper towels to remove excess moisture.

Drain the lentils and transfer them to a food processor. Add chile powder, turmeric, and ¾ teaspoon salt. Pulse until a purée forms, scraping down sides as needed. Transfer to a bowl and mix in the zucchini-onion mixture, parsley, and lemon zest. Toss well to combine.

Heat ghee in a 10-inch cast-iron skillet over medium-high heat. Drop ¼ cup of batter into the hot ghee, flattening with the back of a large metal spoon dipped in ghee to prevent sticking. Repeat to make 4 fritters. Fry until deep golden brown on one side, about 3 minutes. Flip and fry until the other side is golden brown, about 3 more minutes. Transfer to a wire rack set over a paper towel-lined baking sheet to drain. Season with salt immediately. Repeat with remaining batter to make 8-10 fritters.

Serve fritters hot with lemony yogurt on the side.