In a jar or airtight container, add the mashed bananas, rolled oats, milk, yogurt, maple syrup, vanilla, almond extract, salt, and cinnamon if using. Stir well until everything is fully mixed.
Close the container with a lid and place it in the refrigerator for at least 2 hours, but overnight is best for the right texture.
The next day, take the oats out of the fridge and give them a good stir. The oats will have absorbed most of the liquid and become thick and creamy. If the mixture feels too thick, add a small splash of milk and stir again until you reach the texture you like.
Add chopped walnuts on top along with any other toppings you enjoy. Serve cold straight from the jar.