Coarsely grate the zucchini on the hash browns and season with 1/2 teaspoon salt. Let stand for 10 minutes and then squeeze the water out of the zucchini in portions with your hands. Pepper. Cut the onion into rings and chop the garlic. Tear the basil with your hands.
First fry the onion in a pan and when the onion is browned add the garlic. Take both out and set aside. Fry the zucchini in the pan until done. Finally, put the onion, garlic and lemon zest back in and put everything in a bowl. Add eggs, flour and basil, torn with your hands. Salt and pepper. Mix the dough together and add half a tablespoon more if necessary. The mass should no longer be liquid.
Rub a coated pan thickly with a piece of cold butter and dust with a little flour (remove excess flour). Put the zucchini batter in the pan, smooth it out and fry on the stove over a mild heat for 10 minutes with the lid on. Then remove the lid and coat the surface of the frittata well with another piece of butter. Lift the frittata on the edge of the pan with a wooden spoon or similar and loosen. Then fell onto a plate and slide back into the pan to fry the other side. Cover and sprinkle with grated cheese for another 5 - 7 minutes.