Clean the mushrooms, carefully unscrew and chop the stems. Finely chop the onion, press the garlic cloves and dice the prunes.
Mix the chopped mushroom stalks, onion, garlic cloves, prunes, Gouda, parsley and breadcrumbs well and season with salt and pepper to taste. Distribute the mixture on the mushroom heads and place two heads on top of each other.
Wrap a slice of bacon around each compound mushroom (from top to bottom to hold it together) and pin it with a toothpick. Fry the mushrooms all around in a pan with the oil.