Preheat oven to 400 degrees F.
Divide the olive oil, thyme, olives, and tomatoes in the bottom of 12 muffin cups.
Cover with a slice of the onion.
Using a round biscuit or cookie cutter, cut out circles of the puff pastry (the circles should be slightly bigger than the top of the muffin cup since they will shrink in the oven) and place over the onion.
Gently push the pastry over the onions, so they are a snug fit.
Bake for 20 to 25 minutes or until golden brown and well puffed.
Allow to cool for just a moment before inverting onto a tray.
Add the cheese, drizzle with balsamic, add salt and pepper to taste and serve immediately.