Use a glass bowl that fits inside your slow cooker. Stir together the water, milk, steel-cut oatmeal and salt inside the bowl.
Place the bowl in the slow-cooker, add enough cold water to come about halfway up the side of the bowl. Switch on “low” and go to bed.
In the morning, remove the bowl from the slow cooker, add toppings to individual bowls of oatmeal and enjoy!
Refrigerate leftovers to enjoy later. When reheating the oatmeal, add a little warm water or milk.