Add the chia seeds, protein powder, and salt to a jar and mix to combine.
Pour in the milk and vanilla and stir to combine, ensuring no clumps of chia seeds are left at the bottom of the jar.
Fold in the mixed berries.
Place a lid on the jar and refrigerator for at least 6 hours or overnight for best results.
Before serving, optionally top with additional mixed berries and honey or maple syrup.
