Let the puff pastry defrost and preheat the oven to 180°C (350°F).
Slice the mushrooms and cook them in a little bit of oil until reduced. Put them aside.
Add some new oil to the pan and cook the pickled onions until they have a nice colour.
Crush the garlic and add it, along with the parsley and thyme, to the tomato paste.
Start layering all the ingredients on 5 of the puff pastry squares. Starting with the onions, tomato paste, mushrooms and hamburger. Add the bacon slices last, along with a bit of pepper.
Put the remaining squares on top and close your parcels. Make sure to press the edges together securely. I use a fork for this, as it adds a nice look as well.
Make a hole in the top of the pastry to let the steam escape.