Preheat oven to 375 degrees F. Heat olive oil in a large skillet over medium heat. Add chicken thighs and cook for 4-5 minutes until lightly browned.
Transfer the chicken to a plate and set aside. To the same skillet, add onion, bell pepper, chili powder, cumin, and garlic and cook for 2-3 minutes until the onion is transparent.
In a large bowl, combine shredded chicken, onion mixture, sour cream, salsa, green chiles, and cilantro. Mix well to combine.
Pour the chicken mixture, Mexican cheese blend, and corn tortillas (torn into small pieces) into a 9x13-inch baking dish layer by layer. Bake in preheated oven for 25-30 minutes until cheese is melted and bubbly.
Serve warm with desired toppings.