Gather all ingredients. Preheat the oven to 375 F. Spray cooking spray on a baking sheet. Add eight 1 inch pools of olive oil evenly apart. Drizzle with a bit of balsamic vinegar. Add a mushroom slice to the center of each one then top with a bit of onion. Cover each with a rectangle of puff pastry then spray over again with cooking spray.
Bake in the oven for 10 minutes until golden brown then remove and let cool. Carefully remove pastries with a knife and plate. Garnish with fresh thyme and serve with a ramekin of Toby’s Feta Cheese Dressing & Dip. Enjoy!