Prep the chilies. If using the fresh option, preferably roast, skin and seed them. Chop into a small dice. Reserve.
Prep the tomato if using the fresh option, slice and dice. Reserve.
In a large mixing bowl, add the onion, cilantro (optional), RoTel Tomato/Salsa, ½ of sharp cheddar cheese (about ¾ cup), Cream of Mushroom Soup, Cream of Chicken and Sour Cream. With a large spatula or spoon, mix the ingredients thoroughly.
Cut cooked chicken into bite sized cubes and add to the King Ranch mix. Mix thoroughly.
If using fresh tortillas, cut into thin strips or squares. If using fried tortilla chips, crush them slightly and add to the King Ranch Chicken mix. Mix thoroughly.
Using a pre-oiled casserole dish, add the King Ranch Chicken mix. Cover with aluminum foil and place in the oven at 350°F/175°C for 40 minutes.
Remove the casserole from the oven. It should be bubbling away or have an internal temperature of 155°F/68°C. Remove the aluminum foil and add the second half of the sharp cheddar cheese. Return the casserole to the oven for 8-10 minutes or until the cheese is golden brown.
Remove the casserole from the oven and allow to rest for 8 minutes before serving.