Heat an oven to 350°F.
Heat the cast iron skillet over medium on the stove top.
Add the butter to the skillet. When the butter begins to sizzle, add the slaw and cook until tender, stirring occasionally. Remove the skillet from the heat.
Mix the Monterey jack and cheddar cheeses, and sprinkle half the cheese (one cup) over the cooked broccoli slaw.
Spread the shredded chicken over the cheese, then sprinkle on the bacon.
Combine the sour cream, ranch, and water in a bowl, and stir until combined.
Pour the ranch mixture over the ingredients in the skillet.
Sprinkle the remaining cup of cheese over the top.
Place the skillet in the heated oven. Bake until the casserole is completely heated through and the cheese on top begins to brown and bubble, about 30 minutes.
Allow the casserole to rest five minutes before serving.