I just made this up yesterday and my sister and I loved it! So easy. I used the store bought pre-cooked chicken because I was in a hurry but it would be cheaper and better probably to buy the chicken and cook it, tear it into bite sized pieces.
Preheat oven to 400. Drape puff pastry over pie plate. Mix together all ingredients on stove except cheese. Pour over pastry, grate some cheese on top. Gather up the four corners to enclose totally-like an envelope. Brush with beaten egg mixture. Bake 15-20 minutes or so. (use judgement--measurements don't need to be exact).