1package of Schar's gluten-free puff pastryor make your own, see notes
Pull meat off rotisserie chicken, shred it and set it aside.
Preheat oven to 400º.
Heat large pan with avocado oil over medium-high heat. Add onions and cook for two minutes, then add garlic, butternut squash and mushrooms. Continue to cook for an additional 6-8 minutes, stirring often, until mixture is softened.
Add frozen peas, thyme, rosemary, salt and pepper to mixture and continue to cook for an additional minute.
Add 2 cups of chicken broth, bring to a boil, then reduce heat to a simmer. Mix in shredded chicken and allow mixture to simmer for about 10 minutes.
In a small saucepan, melt butter over medium-low heat, then add flour and whisk mixture until incorporated. Add remaining 2 cups of chicken broth to the flour mixture and continue to whisk mixture until incorporated. Turn off heat.
Add contents of saucepan to the filling mixture and combine well. Continue to simmer mixture for another 2-4 minutes, stirring often. The sauce should continue to slightly thicken. Add additional salt and pepper to taste (optional).
Add filling mixture to a large (9x13") casserole dish and set aside.
You can either roll out puff pastry dough to desired size, or simply add the sheet directly to the pan (without rolling). I prefer to simply add the sheet without rolling it for less fuss. If using Schar puff pastry, do NOT add an egg wash mixture as it will burn your puff pastry (trust me!). If making homemade puff pastry, an egg wash will ensure the puff pastry is nice and brown. Each Schar puff pastry package comes with two puff pastry sheets. If your sheet does not fully cover the casserole dish, cut a portion of the other sheet and use it to cover your casserole dish.
Place casserole in the oven and bake for 25-35 minutes. Keep a close eye on the puff pastry to make sure it doesn't burn. (Cover with foil if it starts to burn too quickly.) It may need more or less time depending on the size of the casserole dish and thickness of the puff pastry.
Allow 5 minutes to cool before digging in.
The Schar gluten-free puff pastry may be hard to find in grocery stores. If your local grocery doesn't have it, request it. Schar has a form letter you can download from its website you can use to request this product in your grocery store. I have seen it at Safeway and Whole Foods.GeeFree foods also makes a gluten-free puff pastry.If you can't find store-bought puff pastry, use my gluten-free puff pastry recipe instead.Do not add an egg wash to the top of store-bought puff pastry. It will burn. This recipe is delicious as leftovers too! Store leftovers in your fridge and reheat in your microwave the next day. Delic!