I came up with this while looking for something to do with my leftover turkey from Thanksgiving and going through my fridge. I'm not a big Pot Pie eater, but I couldn't get enough of this. Neither could my family. I threw it all together, but I will write it up as best as I can. This turned out too good not to share.
Heat oven to 400. On a lightly floured surface, roll croissants to fit an 8x11x2 in (or similar) baking dish sprayed with Pam. Gently lay croissants and spread evenly making sure to fit the sides.
In a large bowl, mix all the ingredients except the ritz crackers and butter (reserving some of the shredded cheese). Pour into casserole dish. I personally like to add some crushed ritz crackers in with the mixture. Top with reserved cheese.
Melt the butter in a small saucepan and add 1 package of crushed ritz crackers. Mix well. Sprinkle on top of the chicken mixture. Bake for 15-20 minutes or until croissant crust are brown and mix is bubbly.