Spray a 6-quart slow cooker with non-stick cooking spray. Line the bottom with half of the corn tortilla chips.
In a large bowl, combine 3-4 cooked and diced chicken breasts, 1 (10-ounce) can Rotel , 1 (10.5-ounce) cream of chicken soup,1 (10.5-ounce) cream of mushroom soup, 1 cup chicken broth, and ⅓ cup diced onion. Mix until combined.
Put half of the mixture over the tortilla chips and sprinkle half of the cheese on top. Repeat layers and end with cheese on top.
Cook on LOW for 4-6 hours or HIGH for 3-4 hours. Serve with additional tortilla chips on top, if desired.