Heat oven to 200°. In a small bowl, mix yogurt, lime juice, lime zest and 1/4 tsp of the salt until smooth.
Squeeze shredded zucchini in a clean kitchen towel until most of the moisture is absorbed. In a medium bowl, combine zucchini, scallions, 1/2 cup of the cilantro, the egg, flour, remaining 1 tsp salt and the pepper.
Heat 2 tbsp of the oil over medium-high heat in a large sauté pan. When shimmering, add zucchini mixture in four 1/4-cup portions. Flatten fritters with a spatula until they are 3 inches in diameter. (It will require 3 batches.) Cook fritters 3 minutes, until browned, then flip and cook another 3 minutes. Transfer fritters to a baking sheet and place in oven to keep warm. Continue cooking fritters, adding 1 more tbsp of oil each time. Serve with lime yogurt and garnish with remaining cilantro.