In a 16-ounce mason jar or airtight container, whisk together the rolled oats, protein powder, and chia seeds until evenly distributed.
Add the almond milk, Greek yogurt, lemon zest, lemon juice, and vanilla extract to the dry base.
Stir vigorously with a spoon or whisk until the protein powder is fully dissolved and no dry pockets remain.
Gently fold in the fresh blueberries to avoid crushing them.
Secure the lid on the container and place in the refrigerator for a minimum of 6 hours or overnight.
Remove from the refrigerator, stir well to redistribute moisture, and serve chilled. Add an optional splash of milk to adjust consistency if necessary.