In a blender, combine the rolled oats, milk, Greek yogurt, honey or maple syrup, vanilla extract, mixed berries, and salt. Blend until smooth and creamy.
Pour the blended mixture into individual jars or containers, leaving some space at the top for expansion.
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, stir the oats and add a splash of milk if a thinner consistency is desired.
Top with your choice of sliced bananas, nuts, seeds, or additional berries before serving.