Add sour cream, taco seasoning, and salsa to large mixing bowl. Stir ingredients well.
Add chicken, tortilla pieces, onion, and two cups of cheese to the mixture. Stir well to combine all ingredients.
Coat 9"X13" casserole dish (or 2 1/3 sized pans) with olive oil or cooking spray. Pour enchilada mixture into the dish and spread evenly.
Sprinkle remaining cheese on top of dish, then top with black olives.
To prepare now: Bake at 350°F for 30 minutes or until cheese is melted and bubbly and dish is completely heated through.
To freeze: Wrap casserole dish with plastic wrap and lid and store in freezer. Thaw in fridge overnight and bake at 350°F for 30-35 minutes or until cheese is hot and bubbly and dish is heated through.