Add all the ingredients to a mason jar and mix well with a spoon. Place the lid back on and let it sit in the fridge overnight. I prep this in the evening and it's perfect for breakfast the next day!
For toppings such as fruits, I recommend adding the fruit the morning of, and just letting the oat base soak overnight. One exception to this is adding a mashed overripe banana to the base and letting that sit overnight--it really brings out the banana flavor! It pairs really well with some peanut butter or chocolate protein powder.