Wash the potatoes and boil in water for about 20 minutes. Wash, clean and halve the zucchini and tomatoes. Cut the zucchini into slices. Wash the thyme, dab dry, put some aside for garnishing, chop the rest finely.
Wash the meat, dab dry and cut into cubes. Heat the oil in a large pan and fry the meat until golden brown. Add zucchini and thyme. Fry briefly. Dust with flour and sauté briefly.
Add 350 ml of water and milk bit by bit while stirring. Bring to the boil, stir in broth, simmer for 5 minutes. Drain potatoes, rinse with cold water, peel and halve. Season sauce with salt and pepper.
Spread the potatoes, tomatoes and zucchini meat sauce in an ovenproof dish. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes. Garnish with thyme put aside.