Combine all ingredients in a slow cooker and cook on low for 5-8 hours, depending on the texture of oats that you prefer.Give oatmeal a good stir before serving. Scoop out 1-1.5 cups and add preferred garnish.Store in a sealed container in the fridge for about a week. Warm leftover oatmeal for about 2 minutes in the microwave and add a splash of milk for desired consistency. Enjoy!