In a medium bowl or jar, combine the rolled oats, almond milk, honey or maple syrup, vanilla extract, cinnamon, and salt. Stir until well mixed.
Gently fold in the sliced banana and blueberries. If using Greek yogurt, add it now and mix until combined.
Divide the mixture into two jars or containers with lids.
Cover 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. You can add more milk if you prefer a thinner consistency. Enjoy cold or heat in the microwave for about 30 seconds if you prefer it warm.