Place milk, water, oats and the remaining ingredients (except the optional toppings) in a 2-quart casserole that fits in your slow cooker.
Fill your slow cooker with a couple inches of water and place the casserole on a rack in the slow cooker. (You may also place the casserole on a ring made out of aluminum foil. You don’t want the dish to be sitting on the bottom of the cooker.)
Cook on low for 3 hours. Cool slightly, and then remove the dish from the cooker, cover and refrigerate until ready for breakfast. You may also portion into individual bowls.
In the morning, reheat gently in the microwave and top as desired.