In a mason jar or seal-able container, combine mashed banana, milk, chia seeds, and oats. Shake or mix well.
Decision time: choose which option you want to add into your oats. Mix the rest of the add ins.
Cover or screw lid onto container. Shake it again for good luck. Store in the refrigerator at least overnight and up to 4 days.
Before eating, shake well and give it another stir. Feel free to top with more ingredients - nut butters, fruit, spices, nuts, seeds... get crazy.