Shred zucchinis, onion, and potatoes using a box grater over a clean dish towel. Squeeze out excess liquid from shredded vegetables.
Transfer shredded vegetables to a large bowl. Stir in parsley, dill, Parmesan, matzo meal, sugar, lemon juice, garlic, and eggs. Stir to mix well. Add in salt and pepper to taste.
In a large skillet, heat oil over medium-high. Reduce heat to medium; place mounds of zucchini mixture into skillet in batches. Flatten each with a spatula and cook until golden brown, roughly 1–2 minutes per side.
Remove zucchini pancakes from skillet and place on paper towels to drain excess oil.
Sprinkle with salt and serve warm with sour cream and extra shredded zucchini.