Chop the hard cheese and mozzarella on a fine grater and place in different bowls. Cut the onion into large cubes.
Heat a frying pan with vegetable oil and fry the onion and garlic, add the tomatoes and simmer over medium heat for 20-30 minutes, stirring occasionally.
Break the eggs into a bowl and whisk with a fork or whisk. Then roll each piece of meat first in flour, then in egg and then in breadcrumbs. In the same pan, fry the chicken on both sides for 6-7 minutes until golden brown.
In an ovenproof dish, layer tomato sauce, then a layer of chicken, then sauce again. Spread the cheese on top, then layer the chicken, sauce and cheese again. Sprinkle with dried oregano.
Bake the chicken for 15-20 minutes at 180°C.