Peel and wash the potatoes and cook them in salted water for about 20 minutes. In the meantime wash and halve the cherry tomatoes. Dice the dried tomatoes. Peel and chop the onion. Wash the oregano and remove the leaves from the stems.
For the tomato sauce, heat oil in a saucepan. Sauté the onion until transparent. Add the chopped tomatoes, dried tomatoes and oregano, bring to the boil and simmer for about 5 minutes. Season with salt, pepper and 1 pinch of sugar. Crumble the feta. Stir cream and approx. 2⁄3 Feta into the sauce.
Peel the cucumbers, halve them lengthwise and remove the seeds. Drain potatoes. Add butter and milk and mash everything roughly. Season to taste with salt and nutmeg. Spread mashed potatoes into the cucumbers.
Put the tomato sauce and cherry tomatoes in a casserole dish. Place the cucumbers on top and sprinkle with the rest of the feta. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer) for 35-40 minutes.