Preheat your oven to 375°F (190°C) and grease a 9x12-inch casserole dish with olive oil.

In a skillet over medium heat, add olive oil and sauté the diced onion for 3-4 minutes until translucent.

Add minced garlic, chili powder, and ground cumin, cooking for an additional minute until fragrant.

Incorporate the cooked shredded chicken, heating through for 2-3 minutes.

In a separate bowl, mix together salsa verde and sour cream until smooth.

Begin layering in the casserole dish: start with one-third of the salsa mixture, half of the tortilla halves, half of the chicken mixture, and 1 cup of cheese.

Repeat the layering with another one-third of salsa, remaining tortillas, chicken, and top with the remaining cheese.

Bake for 15-20 minutes until cheese is melted and bubbly, and top is golden.

Let the casserole cool for a few minutes before serving.