Preheat oven (electric cooker: 225°C/circulating air: 200°C/gas: level 4). Place bread on a baking tray lined with baking paper.
Clean the mushrooms and cut them smaller. Peel onion and cut into rings. Halve the bacon, fry in a pan without fat and remove. Fry the mushrooms and onion in the frying fat, season with salt and pepper.
Meanwhile wash the herbs, shake dry and chop. Mix with sour cream, salt lightly. Spread on the flatbread. Cover with mushrooms and bacon, crumble cheese over it. Bake in a hot oven for 7-10 minutes.