In a mixing bowl, mash the ripe bananas with a fork until smooth.
Add the almond milk, peanut butter (if using), ground cinnamon, and vanilla extract to the mashed bananas. Stir until everything is well combined.
Add the rolled oats to the mixture. Stir thoroughly to ensure the oats are fully coated with the banana mixture.
If desired, drizzle in the maple syrup and mix well. Taste and adjust the sweetness as needed.
Transfer the mixture into a jar or airtight container and seal it. Place it in the refrigerator overnight (or for at least four hours).
In the morning, give your Banana Overnight Oats a good stir. Enjoy it cold or heat it in the microwave for a warm breakfast.