In a large skillet, heat olive oil over medium heat and sauté chopped onion until softened, then add minced garlic and cook for another minute until fragrant.

In a large bowl, combine the shredded chicken, softened cream cheese, diced green chiles, salt, and pepper, mixing until well combined.

Spread half of the enchilada sauce in the bottom of a 9x13 inch baking dish. Layer with half of the torn tortillas, followed by the chicken mixture, and then sprinkle with half of the shredded cheese. Repeat the layers with the remaining tortillas, sauce, and cheese.

Bake in a preheated oven at 375°F (190°C) for 25-30 minutes, or until the casserole is bubbly and the cheese is melted and lightly golden. Let stand for a few minutes before serving.