Pre-heat your oven to 175 degrees (warm). Place an oven proof cooling rack on top of a large sheet pan and place inside your oven to warm. This will be where you keep your pancakes warm as you make your batches on the stove top.
Place grated zucchini in cheesecloth or a double layer of strong paper towels over a large colander. With your hands or the back of a large spoon, press down on the zucchini to remove as much moisture as possible. Do this a few times until the zucchini begins to dry out a bit and you see liquid coming through the colander. Now take your strained zucchini and add it to a large bowl. Next, add your eggs, and onion and mix well. In a small bowl, combine your flour, Parmesan cheese, baking powder and, salt. Mix this into your zucchini mixture until batter is just moistened.
Heat 2-3 tbsp of vegetable oil in a large skillet over medium-high heat. Drop rounded spoonfuls of zucchini batter on to the hot skillet and cook until golden brown, about 3 minutes per side. Blot pancakes on a paper towel-lined plate and then place in warm oven while you make the rest of your pancakes.
Repeat Step 3 until all of your batter is gone.
Serve pancakes with a generous dollop of sour cream on the side and garnish with the extra chopped green onions.