In a large mixing bowl, combine the rolled oats, almond milk, chia seeds, honey or maple syrup, vanilla extract, cinnamon, and salt. Stir well until all ingredients are fully combined.
Divide the mixture evenly into two jars or containers with lids.
Add a layer of mixed berries on top of each jar, then sprinkle the chopped nuts over the berries.
Seal the jars or containers and refrigerate overnight (or for at least 4 hours) to allow the oats and chia seeds to absorb the liquid and thicken.
In the morning, stir the mixture before serving. Enjoy cold or warm it up in the microwave for 30 seconds if desired.