Crock Pot Method: I prefer the oven for a crispy topping, but you can also layer the ingredients in your slow cooker if that’s easier. You will need to cook the casserole on LOW for about 3-4 hours or on HIGH for 1-2 hours, just until everything is heated through and bubbly. Add the final Doritos on top just before serving (you don’t want to add them too soon or they’ll get soggy).