Peel onion and cut into rings. Clean and slice the mushrooms. Wash thyme, shake dry and pluck leaves from the stalks. Cut mozzarella into thin slices.
Roll out the roll blanks lengthwise on a floured work surface. Place on a baking tray lined with baking paper. Spread 2 tablespoons of tomato sauce on the dough. Cover with salami, mushrooms, onion and mozzarella.
Spread some thyme on it. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 10 minutes.