Remove the puff pastry from the box and wrapper, and allow to thaw on the counter for about 25 minutes. You want the pastry to be pliable, but not warm. Lay the pastry sheets on a large baking sheet lined with parchment.
In a medium frying pan, melt the butter over medium low, and cook the onions down until soft; about 15-20 minutes.
Spread the pesto in the middle of one puff pastry sheet, and the bruschetta in the middle of the other.
Top with spinach/kale, cheese, chicken, and onions.
Like you are wrapping a present, fold the two top "flaps" over each other. Repeat with one bottom flap, and then the other. Pinch the dough together a bit to secure it.
Bake at 400 degrees for 23 minutes, or until the pastry is golden brown and flaky. We have found it is easiest to cut into portions with a pizza cutter. Serve hot with a side salad or delicious grilled veggies.
Notes
Due to the time needed for thawing the pastry (20-30 min at temperature), it would be ideal to prep this in the morning before leaving for work.Put in an air-tight container in the fridge, and bake when you get home.