Pour the flour into a bowl and make a depression in the middle. Crumble yeast into it. Add about 5 tablespoons of lukewarm water. Mix with some flour to a pre-dough. Cover and let it rise for about 15 minutes.
Drain the cheese and cut into slices. Peel onions, cut into thin rings. Clean, wash and slice tomatoes and mushrooms. Season strained tomatoes with salt, pepper and thyme.
Add 150 ml lukewarm water and oil to the pre-dough. Knead everything into a smooth dough. Leave to rise for another 15 minutes. Quarter the dough, roll out round. Place on a baking tray. Spread with strained tomatoes.
Add cheese, onions, mushrooms and tomatoes. Bake in the preheated oven (electric cooker: 225 ° C/ gas: level 4) for about 30 minutes. Add Parma ham 5 minutes before the end of the baking time. Garnish with thyme if desired.