In a medium bowl, combine the rolled oats, cocoa powder, and salt. Mix well to ensure the cocoa powder is evenly distributed.
In another bowl, whisk together the milk, peanut butter, maple syrup, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until fully combined. If using chocolate chips, fold them in at this stage.
Divide the mixture evenly into two jars or containers with lids.
Cover and refrigerate overnight (or for at least 4 hours) to allow the oats to soak and soften.
When ready to serve, give the oats a good stir and top with sliced bananas or berries if desired.