Assemble the Casserole: Coat the bottom of the 9×13 baking dish with 1/3 cup of enchilada sauce. Then place a layer of 4 tortillas in the dish (they will overlap some). Next, add approximately a heaping cup of the chicken filling and spread out with a spatula or the back of spoon. Then pour on 1/3 cup of enchilada sauce. Repeat the process until all of the tortillas are used, you will have 3 layers ending with chicken filling on top.
Pour the remaining enchilada sauce over the casserole and then sprinkle with an even layer of the remaining 2 oz of shredded pepper jack and 4 oz Monterrey cheese over the casserole.
Bake at 400 degrees for 20-25 minutes until cheese is melty, bubbly, and beginning to brown.
Garnish the enchilada casserole with chopped cilantro, diced red onion, sliced avocado, sliced jalapeño, sour cream or Greek yogurt, and fresh limes.