Shred zucchini with a box grater or with a food processor attachment. I recommend using a larger grate, but finely grated zucchini also works.
Add the shredded zucchini to a bowl, and sprinkle with 1 teaspoon of salt. Allow to sit for 10 minutes to allow water to be released.
Add zucchini to a cheesecloth or thin dish towel, and squeeze to release excess water. I was able to squeeze out about 1 1/2 cups of water.
Into a large bowl, add the zucchini, sweet corn kernels, green onions, and egg. Mix to coat the vegetables in the egg.
In a medium bowl, add the almond flour, arrowroot, parmesan cheese, baking powder, and remaining 1/2 teaspoon of salt. Mix well.
Stir the dry ingredients into the bowl with the zucchini mixture, and stir to evenly mix in.
Heat a skillet over medium heat. Drizzle to coat with avocado oil. Scoop the zucchini and corn batter into a 1/2 cup measuring cup, packing it in tight. Add the batter onto the hot skillet.
As the batter begins to cook, press down lightly with a spatula, so that the tops are flattened but the fritters still are about 3/4 of an inch thick. Cook for about 10 minutes, until browned, and then flip to cook the other side for about 10 minutes. I find these cook the best when in a skillet with a lid for the first 10 minutes, to allow the egg to start to firm up.
Serve hot with sour cream on the side, if desired.