Preheat oven to 375 degrees. Lightly spray the bottom of a 9x13-inch dish with oil or cooking spray, set aside.

In a large skillet set over medium-low heat, add the oil. Once hot, add the onion and saute until tender, about 3 minutes. Add the garlic and saute until fragrant, about 1 minute.

Pour in chicken broth, add chili powder, oregano, cumin, coriander, salt, and pepper. Bring broth to a simmer and add the chicken. Simmer for 5 minutes, then remove from the heat and set aside.

Pour 1/4 cup of enchilada sauce into the bottom of the baking dish, spread into an even layer. Layer the bottom of the dish with six tortillas. Spread 1/3 cup of the sour cream over top, followed by half of the chicken mixture, 1/4 cup of cheese, and a 1/4 cup of enchilada sauce. Repeat by layering six tortillas, spread 1/3 cup of the sour cream over top, followed by the remaining chicken mixture, 1/4 cup of cheese, and a 1/4 cup of enchilada sauce.

Layer the remaining 6 tortillas on top, followed by the remaining enchilada sauce and remaining cheese. Sprinkle green onions over top and cover with foil.

Place in the oven and bake for 30 minutes, then remove the foil and continue baking for an additional 10 minutes.

Remove from the oven and allow to sit for 10 minutes before serving. Garnish with cilantro, if desired.