Pre-heat oven to 350° (180° celsius).  Line a cookie sheet or 2 with parchment paper.In a small frying pan add olive oil, sliced mushrooms, salt, oregano and parsley, cook on medium, stirring occasionally until mushroom have browned slightly and are tender.  Remove from heat.Roll out Puff Pastry (if frozen thaw completely), and cut out circles with a round cookie cutter (2.5 inch / 6.5 centimeter) top each round with a teaspoon or 2 of white sauce, spread with the back of the spoon, top with 2 or 3 mushroom slices and sprinkle with grated Parmesan cheese or cheese of choice.  Bake for approximately 20 minutes.  Serve warm.  Enjoy!