Combine all ingredients in a large jar or container. Stir everything together until well combined.
Wait 2-3 minutes then stir everything again, breaking up any clumps of oats or chia seeds that have formed.
Cover the mixture and place it in the refrigerator for at least an hour or until the chia seeds and oats have absorbed the oat milk and a thicker consistency has formed.
Notes
These overnight oats can be stored in the refrigerator in a covered container for up to five days.