Wash the potatoes thoroughly and cook in boiling water for about 15 minutes. Peel and chop the onion. Heat the oil in a large pan and fry the minced meat until crumbly. Add onion and herbs and fry briefly.
Add tomato paste and sweat briefly. Add the strained tomatoes, season with salt and pepper and simmer for about 10 minutes on a low heat. Drain potatoes, rinse with cold water and peel.
Wash, clean and slice the zucchini. Whisk milk and eggs, season with salt and nutmeg. Season the minced sauce once again, cut the potatoes into slices. Layer potatoes, zucchini and minced sauce in an oven dish.
Pour egg milk over it and sprinkle everything with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Garnish with oregano.