In a medium bowl or jar, combine the rolled oats, almond milk, honey or maple syrup (if using), vanilla extract, ground cinnamon, and a pinch of salt. Stir well to combine.
Gently fold in the sliced banana and blueberries, ensuring they are evenly distributed throughout the mixture.
If using Greek yogurt, add it to the mixture and stir until well combined.
Cover the bowl or jar with a lid or plastic wrap 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 a splash of milk if you prefer a thinner consistency. Enjoy cold or heat in the microwave for 30-60 seconds if you prefer it warm.