Coat inside of 3.5 to 4 quart slow cooker with cooking spray. If your slow cooker is larger, use a 5 cup or larger glass baking dish or measuring cup placed inside your slow cooker, surrounded by room temperature water nearly to the top of your glass container.
Add all ingredients into slow cooker or glass container. Mix well, cover slow cooker, and cook on low for 7 to 8 hours. Spoon oatmeal into serving bowls. Stir in additional dairy-free milk or add sliced apples as a topping, if desired. Leftovers can be stored in the refrigerator for later that week or in the freezer for the future.
To reheat single servings: Put 1 cup of cooked oatmeal in microwave proof bowl. Add 1/3 cup dairy-free milk. Microwave on high for 1 minute; stir. Cook for another minute, or until desired temperature.