Add all ingredients into a large mason jar or any glass container and stir until evenly combined.
Cover and store in the refrigerator for at least 6 hours or up to 2 days. Top with sliced bananas, chopped walnuts before serving.
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Notes
Use only rolled oats. Instant oats will turn mushy and steel cuts will remain too hard and difficult to digest.Use gluten free oats to make it gluten free.