Rinse the mushrooms under running water and drain them (they don't have to be perfectly dry, as a little excess water will help steam them).
Heat the olive oil in a pan over medium heat. Add the onion and bacon and cook for a few minutes, seasoning well with salt and pepper. Add the mushrooms, chile, and vinegars and stir well. Cover and simmer gently for 25 minutes. Remove the pan from heat and stir in a generous glut of extra-virgin olive oil.
Once cool, mix in the parsley leaves and leave to marinate for a few hours at room temperature before eating. Drain off some of the liquid, if you like (the mushrooms can release quite a lot of liquid), and taste to check the seasoning.