Preheat oven to 350 degrees F. Spray a 13x9 baking pan with non-stick cooking spray.
In a medium size bowl, combine sour cream and taco seasoning and mix well. Chop or shred chicken into small pieces. Add to sour cream mixture and stir to combine.
Pour approximately 1/2 inch of enchilada sauce into the baking dish, making sure to fully cover the bottom of the dish.
Place a layer of tortillas onto the enchilada sauce to cover the bottom of the pan. This will be approximately 6 enchilada pieces.
Top with 1/2 the chicken and sour cream mixture, then sprinkle 1/3 of the shredded cheese on top, followed by 1/3 of the remaining enchilada sauce. Repeat for a second layer.
Dip or coat the remaining tortillas with enchilada sauce, then place a final layer on top. If there is any enchilada sauce remaining, drizzle over top. Top with remaining cheese.
Cover baking pan with foil and bake for 45 minutes. Allow to cool for approximately five minutes prior to serving. If desired, garnish with tomatoes, green onions, black olives and additional sour cream.