At least 4 hours before you’re ready to fry the pancakes, peel 1 of the zucchini and then shred all of them using a grater. Bundle the shreds into a clean kitchen towel or cheesecloth and place in a colander set over a large bowl. Salt the zucchini evenly, and then weigh down the zucchini with a heavy plate or bowl. Place the whole thing in the refrigerator and let the zucchini drain for at least a few hours.
When you’re ready to cook the pancakes, preheat the oven to 200F.
Heat the oil in a cast-iron skillet (or any heavy-bottomed frying pan) over high heat. Pat the zucchini dry to remove any remaining moisture, then transfer to a dry mixing bowl. Add 2 of the eggs and 1/4 cup of the flour, then mix and add the remaining egg and flour if the mixture is still not coming together fully. Stir in the garlic, cayenne, and onion powder.
Add the zucchini batter to the pan in spoonfuls, making sure to fry only a few at a time so as not to crowd them. Let the pancakes cook for 3-4 minutes on each side, and line a plate with paper towels for draining.
After each batch of pancakes has drained slightly, transfer them to a baking sheet and put them in the oven to keep warm and crisp-up. Serve immediately after the batches are complete.