Prepare the Zucchini: Place the grated zucchini in a colander over the sink. Sprinkle with a pinch of salt to draw out moisture. Let sit for 10 minutes, then squeeze out as much excess water as possible using your hands or a clean kitchen towel.

Mix the Ingredients: In a large bowl, combine the drained zucchini, beaten eggs, minced onion, flour, Parmesan cheese, mozzarella cheese, salt, and pepper. Stir until well mixed.

Heat the Oil: Heat vegetable oil in a large skillet over medium-high heat.

Form the Patties: Scoop about 1/4 cup of the mixture per patty into the skillet. Flatten slightly with the back of a spoon or spatula to form patties.

Cook the Patties: Cook each patty for 2-3 minutes per side, or until golden brown and cooked through. Transfer to a plate lined with paper towels to drain excess oil.

Serve Hot: Serve the zucchini patties warm, optionally topped with a dollop of sour cream or paired with your favorite dipping sauce.