Heat the oil in a pan and fry the mince in it at medium heat for about 5 minutes until golden brown all around. In the meantime clean, wash and cut the zucchini into pieces. Remove the minced meat from the pan and set aside.
Fry the zucchini in the cooking fat for 3-4 minutes. Season with salt and pepper. Deglaze with stock and cream and bring to the boil. Thicken with sauce thickener and season with salt and pepper. Add minced meat and heat up again.
Wash thyme and parsley, dab dry and chop or cut into strips. Add to the sauce and stir in. Bring milk, 300 ml water and 1/2 teaspoon salt to the boil, remove from heat and add the mashed potato powder while stirring.
Add 5 g butter and melt in it. Put the mashed potatoes into a greased casserole dish. While doing so, pull the mixture up a little at the edge. Put the zucchini-mett sauce in the middle. Sprinkle with cheese.
Spread the rest of the butter in flakes on top. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for 20-25 minutes. Serve sprinkled with diced tomatoes as desired.