Peel and finely dice the onions and garlic. Heat the oil in a large pan. Fry the minced meat in it in 2 portions until crumbly. Fry the onions and garlic briefly at the end and add the minced meat again. Add tomato paste and 2 tsp. oregano and sauté. Deglaze with 200 ml water, bring to the boil and season with salt and pepper. Stir 50 ml water and starch until smooth and pour into the sauce. Bring to the boil again and simmer for about 2 minutes.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Peel and wash sweet potatoes and slice or slice them thinly. Crumble feta finely. Season cream with salt and pepper.
Pour some cream on the bottom of a casserole dish. 1⁄3 Layer sweet potato slices, half minced meat and half feta. Again 1⁄3 Add sweet potatoes, repeat layering and finish with sweet potatoes. Pour half the cream over the top two sweet potato layers. Cut the mozzarella into slices and spread on top. Bake in a hot oven for about 50 minutes. If necessary, bake in the last approx. 1