Combine all of the ingredients in a 12 to 16-ounce bowl or jar, mixing until well combined.
Cover and refrigerate overnight or a minimum of four hours.
Remove from the fridge, stir the oatmeal, and serve. See Notes for topping ideas.
Notes
Topping suggestions: berries (pictured), banana, peaches, peanut butter, almond butter, sliced almonds (pictured), granola, hemp hearts, chocolate chips.Storage: Refrigerate in an airtight container for up to 5 days. The old-fashioned oats will become softer over time.