Peel the potatoes and the carrots. Grate them into a bowl. Add zucchini, onion, flour, salt, parsley and egg yolks into a bowl. Stir to combine. Place egg whites into a bowl and beat until stiff peaks form. Fold through the vegetable mixture. Heat a large pan over medium heat. Add a little oil. Add 1/3 of the mixture and cook for 5 minutes. Cook 4 at a time. Turn and cook a further 5-8 minutes and repeat until all the mixture is cooked.