In a medium bowl, combine the rolled oats, milk, Greek yogurt, honey or maple syrup, vanilla extract, cinnamon, and a pinch of salt. Stir until well combined.
Divide the mixture evenly into two jars or airtight containers.
Top each jar with mixed berries, pressing them gently into the oats.
Seal the jars or containers and refrigerate overnight (or for at least 4 hours) to allow the oats to soak and soften.
In the morning, give the oats a good stir and add additional milk if you prefer a thinner consistency. Enjoy cold or warm them up in the microwave for about 30 seconds if desired.