1) Using a 2-quart bowl that fits inside your slow cooker with the lid on, add steel cut oats, milk, chopped apples, brown sugar, pure maple syrup, raw honey, salt, and vanilla to this bowl and stir together.
2) Fill the slow cooker about halfway full with water. Set the bowl filled with ingredients in the slow cooker filled with water. Adjust the water level, so it reaches about an inch below the height of the outside of the oatmeal bowl.
3) Place the lid on the slow cooker and set on low for 7 to 9 hours. Enjoy in the morning!