In a 16-ounce glass jar or airtight container, mash the half banana until a smooth paste forms.
Add the peanut butter, maple syrup, vanilla extract, and sea salt to the banana and whisk with a fork until integrated.
Pour in the rolled oats, chia seeds, milk, and Greek yogurt.
Stir the mixture vigorously until all ingredients are evenly distributed and no dry oat pockets remain.
Seal the container with a lid and place in the refrigerator for a minimum of 6 hours, or ideally overnight.
Before consumption, remove the lid, stir the contents thoroughly, and garnish with additional banana slices or a drizzle of peanut butter if desired.