Heat the olive oil in a large skillet over medium heat. Once heated, add in the onion and salt and cook for a couple minutes until softened. Stir in the garlic, chili powder, and cumin and cook for another minute. Stir in the chicken until well incorporated and take the pan off the heat.
In a large bowl, combine the salsa verde and sour cream. Stir until the sour cream is fully incorporated.
Layer 3/4 cup of the salsa verde mixture on the bottom of a greased 9x12 casserole dish. Top with 8 tortilla halves. Then, layer on half of the chicken mixture, 1 cup of salsa verde, and 1/2 cup cheese. Repeat with another round of 8 tortilla halves, the remaining chicken, 1 cup salsa verde, and 1/2 cup cheese. Finish with a final layer of 8 tortilla halves, the remaining salsa verde, and remaining cheese.
Bake for 15-20 minutes until the cheese has melted and the sauce is bubbling. Add on optional toppings and serve.
Grease your baking dish before adding the casserole ingredients so that it is easy to remove and serve.
You can use shredded chicken breast, thighs or a mixture of both.
Bake the casserole in a fully pre-heated oven so that it cooks through evenly.