Add oats and chia seeds to blender and blend on high until you have the texture of a fine flour.
Add the milk, yogurt, blueberries, and all remaining ingredients except the sweetener.
Blend on high until the mixture is smooth, scraping down the sides and blending again, as necessary. It is helpful to stir down to the bottom to make sure the oat mixture is fully incorporated. Taste and sweeten to your liking. Blend again to distribute.
Transfer the smoothie to a jar or other lidded container. Refrigerate overnight or at least four hours. Will keep 2-3 days in the refrigerator.
May be frozen. First allow the mixture to soak for at least four hours in the refrigerator.