Combine the rolled oats, mashed banana, peanut butter, cinnamon, and Himalayan salt in a mixing bowl.
Pour in the milk gradually, stirring as you go, until the mixture is well combined and slightly thickened.
Mix thoroughly until all ingredients are evenly incorporated, with the oats and banana fully coated in the peanut butter mixture.
Transfer the mixture to a jar or container with a lid, smoothing the top with the back of a spoon.
Seal the container and refrigerate overnight, allowing the oats to soften and flavors to meld.
In the morning, give the oats a gentle stir to loosen the mixture and check the consistency.
Scoop the oats into bowls, garnish with extra banana slices or a drizzle of peanut butter if desired, and enjoy!