Add all ingredients (except for the cinnamon swirl ingredients) to a bowl or jar and mix or shake well until thoroughly combined.
Refrigerate for at least 4 hours or overnight.
To add the cinnamon swirl, melt the butter in a small dish, then stir in the brown sugar and cinnamon. Swirl into the top of the oats either before refrigerating or just before eating.
Notes
Nutrition is calculated with 1% milk and non-fat plain Greek yogurt and includes the cinnamon swirl topping.