Preheat the oven to 400 degrees F.
Spray a 9 X 11 inch baking pan with cooking spray.
In a large bowl, mix the tomatillo salsa verde with the sour cream.
Spread 1 cup of the sauce on the bottom of the pan.
Layer 6 of the small tortillas on the bottom of the pan.
Spoon 1 ¼ cups of the sauce over the tortillas then layer in the shredded chicken, butternut squash, and black beans.
Top with some of the shredded cheese and repeat the process 2 more times.
Set aside the last layer of cheese.
Cover the pan with a piece of aluminum foil sprayed with cooking spray and bake for 60-70 minutes.
Remove the foil and top with the remaining cheese and bake until melted, about 10 more minutes.
Remove from the oven and top with sliced olives, green onions, and cilantro.
Garnish with sour cream, sliced avocado, and pickled sweet and hot jalapeños.
Optional: Sprinkle Cotija cheese on top for a tart cheese burst of flavor.