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

In a medium skillet, heat olive oil, add chopped onion and salt. Cook until softened, about 5-7 minutes.

Add minced garlic, chili powder, and cumin to the skillet. Stir and cook for an additional minute.

Stir in shredded chicken and cook for 3-4 minutes until warmed through.

In a mixing bowl, combine salsa verde and sour cream. Whisk until smooth.

Spread some salsa verde mixture at the bottom of the greased casserole dish. Layer with corn tortillas.

Add half of the chicken mixture and pour 1 cup of salsa verde mixture over it, then top with half of the cheese.

Repeat the layers with remaining tortillas, chicken mixture, salsa verde, and cheese.

Place remaining tortillas, salsa verde mixture, and cheese on top for the final layer.

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

Allow to cool for 10-15 minutes before serving. Top with cilantro or avocado if desired.