Grate the zucchini on the large holes of a box grater. Place on a kitchen towel and squeeze out excess moisture.

In a large bowl, whisk the eggs. Add the grated zucchini, scallions, garlic, dill, lemon zest, salt, and several grinds of pepper. Add 1½ cups of the panko, sprinkle in the flour, and fold to combine. Place the remaining ¾ cup panko in a shallow dish and set aside.

Preheat a cast-iron skillet to medium heat. Use a ¼-cup measuring cup to form the zucchini mixture into 14 to 16 thin patties. Place each into the reserved panko and coat well. The mixture might seem loose at this point, but the patties will firm up as they cook.

Coat the skillet generously with oil. Cook the patties for 2 to 3 minutes on the first side, flip, and cook for 2 to 3 more minutes, or until well browned, working in batches as necessary. Transfer to a paper towel-lined plate or baking sheet to drain. Season to taste and serve with the sauce.