Divide rolled oats, chia seeds, flax seeds, and protein powder among 6 16-ounce glass jars.
Top each jar with a cup of frozen mixed berries.
Place a lid on each jar and freeze for up to 30 days.
When you're ready to enjoy your smoothie, remove jar from the freezer and run under warm water for a minute or so to begin to thaw just the edges of the berries and the smoothie base. This just makes it easier to pour.
Dump all contents of the jar into a high-powered blender jar. Pour about ½ a cup of almond milk (or milk of choice) into jar and swish it around to get anything you may have missed. Pour into the blender jar.
Top with 1-2 Tablespoons of maple syrup, ice cubes if you're opting for a thicker and colder smoothie, and blender on high until completely smooth, about 1 minute and 30 seconds. Depending on how thick of a smoothie you like, if you're using a Vitamix, the damper stick really comes in handy here.
Once your smoothie is completely blended, taste for sweetness, and add more syrup if necessary. Otherwise, pour back into the jar you originally used or another glass, and enjoy!