Preheat oven to 400 degrees.
Saute onion in olive oil for 3-5 minutes or until translucent.
Add mushrooms and continue sauteing for 2-3 additional minutes.
Add broccoli and chicken and continue cooking for 2 more minutes. Set aside.
Line a large baking sheet with parchment paper.
Carefully unfold thawed puff pastry and cut into four squares.
Roll each square out slightly to make a rectangle.
Repeat with second puff pastry.
Divide filling equally among puff pastry rectangles.
Top with shredded cheese.
Fold the sides over to close making sure to pinch the edges close.
Bake for 20 minutes or until puffs are golden brown.
Cool for 2-3 minutes before serving.