Preheat oven to 400°F / 200°C.
Lightly spray a 9x9 baking dish with nonstick cooking spray or brush it with some oil.
In a large bowl whisk together sour cream, salsa, cream cheese, and ground cumin. Gently fold in beans.
Spread about 1/2 cup of the sour cream mixture out in the bottom of the prepared pan.
Layer on 1/3 of the tortilla strips, 1/2 of the chicken, 1/3 of the remaining sour cream mixture, and 1/3 of the cheese. Repeat with remaining ingredients, ending with a layer of tortilla strips, sour cream, and then cheese on top.
Scatter diced green chilis over the casserole.
Spray some foil with some nonstick cooking spray (to prevent sticking) and place it over the casserole, closing to seal.
Bake, covered, for 25 minutes.
Remove foil and continue baking until the edges are golden brown and the filling is bubbling, about 20 minutes more.
Let cool for 5 minutes before slicing and serving. Top with cilantro leaves and / or chopped avocados if you'd like. Serve with extra salsa verde and, if you’d like, with tortilla chips for scooping.