Preheat oven to 350 degrees. Spray a 2.5 qt dish with cooking spray (a little smaller dish than a 9X13).
In a large bowl, combine the cooked chicken (shredded or diced), cooked and crumbled bacon, spaghetti squash, and ranch sauce until the sauce evenly coats the ingredients. Once combined, pour the mixture into the prepared baking pan. Then top with mozzarella cheese.
Bake at 350 degrees for 25-30 minutes, or until hot and bubbly. For the last remaining minutes, place the dish on the highest baking rack and turn on the broiler. Cook under the broiler until the cheese begins to bubble and brown. Watch carefully, however, because it can burn quickly!
Remove the oven, allow to cool for 5-10 minutes, and then serve!