Peel and dice the onions and garlic and sauté in the oil. Add the minced meat, fry for about 5 minutes. Stir in tomato paste, tomatoes with juice and oregano and simmer for about 20 minutes. Fold in the parsley, season everything vigorously.
Clean the zucchini, peel the potatoes, wash both and cut into slices. Pre-cook the potatoes for about 10 minutes. Grease a baking dish with butter. Layer alternately the potato slices, minced meat, zucchini and cheese until the ingredients are on top. Finish with potatoes.
Preheat the oven to 180 °.
Melt the butter, sweat with flour, pour in the milk, bring to the boil, season. Pour into the tin, bake for about 50-60 minutes.