Defrost spinach at room temperature. Wash and clean the zucchini and tomatoes. Quarter zucchini lengthwise and cut into slices. Cut tomatoes in half horizontally, remove seeds and dice flesh. Peel and dice onion and garlic
Defrosted spinach squeeze and chop roughly. Heat the oil, fry the onion and garlic for about 6 minutes. After about 3 minutes add zucchini, tomatoes and spinach. Season to taste with salt, pepper and nutmeg.
Remove the vegetables from the pan and let them cool down a little. Dice cheese and mix.
Unroll the dough, place it on the floured work surface with the baking paper side facing upwards and remove the baking paper. Spread the vegetable mixture on the long side of the dough to form a strip of about 10 cm wide.
Spread the cheese, except for something to sprinkle on it, in a strand. Roll up and form a ring on a baking tray lined with baking paper. Sprinkle with the rest of the cheese.
Bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see manufacturer) for about 20 minutes.