In A Medium Bowl, Combine The Zucchini, Eggs, Onion, Flour, Parmesan Cheese, Mozzarella Cheese, And Salt. Stir Well Enough To Distribute Ingredients Evenly. Heat A Small Amount Of Oil In A Skillet Over Medium-High Heat. Drop Zucchini Mixture By Heaping Tablespoonfuls, And Cook For A Few Minutes On Each Side Until Golden.