Sprinkle the grated zucchini with about 1 teaspoon of salt and let sit in a colander in the sink for about 5 minutes. Remove the excess moisture from the zucchini by squeezing the liquid out with paper towels. Whisk eggs in a large bowl; add the zucchini, flour, thyme, tarragon, dill and green onions. Mix to combine. Fold in the feta and walnuts. Heat oil in a large skillet over medium heat. Cook fritters in two batches. Drop six mounds of batter (2 tablespoons each) into the skillet. Flatten slightly. Cook, turning once, until browned, 4 to 6 minutes on each side. Transfer to a plate and sprinkle with salt. Repeat with remaining batter. Serve immediately, with plain yogurt on the side. Mix some additional herbs in the yogurt if desired.