Spray the insert of the slow cooker liberally with cooking spray.
Heat 1 tablespoon of butter or coconut oil in a medium saute pan. Once the butter melts, then add in the steel cut oats.
Cook for 1-2 minutes or until fragrant and toasty.
Add the oats, water, milk, pure vanilla extract, ground cinnamon, and salt to the slow cooker. Give it a couple of stirs.
Cover and cook on low for 4 hours and then on warm for 2 hours. If you can stir it a couple of times while it cooks, it will help prevent the oats from sticking and burning.
Serve with your favorite sweetener and toppings.