Zucchini and dill complement each other beautifully, so there’s dill in the dipping sauce here as well as in the batter. The cornmeal ensures a nice crispy crust; for a bit more chew, try the variation made with whole grains.
Heat the oven to 275 degrees. Combine the yogurt, lemon juice, and 2 tablespoons of the chopped dill (or ½ teaspoon dried). Sprinkle with salt and pepper, then taste and add more salt or lemon.
Squeeze the zucchini dry with your hands or a towel and put it in a large bowl. Add the onion, remaining 1 tablespoon fresh (or ½ teaspoon dried) dill, egg, and cornmeal; mix well and sprinkle with salt and pepper. (You can prepare the batter ahead of time to this point and refrigerate for up to a couple hours before cooking.)
Put about ¼ inch oil in a large skillet over medium-high heat. When it’s hot, drop spoonfuls of the zucchini mixture into the oil and spread them out a bit. (Work in batches to prevent overcrowding and transfer the finished fritters to the oven until all are finished.) Cook, turning once, until golden on both sides and cooked through, about 5 minutes. Serve hot or at room temperature with the yogurt sauce.