In a medium bowl or large jar, combine the milk, pumpkin puree, Greek yogurt, maple syrup, and pumpkin pie spice. Whisk thoroughly until the pumpkin is fully incorporated and the mixture is a smooth, uniform orange.
Add the rolled oats and a pinch of salt to the bowl. Stir with a spoon until every oat is coated in the creamy pumpkin mixture. The salt is non-negotiable—it balances the sweetness and enhances the spice flavors.
Pour the oat mixture into a clean mason jar or any airtight container. Secure the lid tightly. Place the jar in the refrigerator and let it rest for at least 6 hours, but overnight (8-12 hours) is ideal. The longer it sits, the creamier and more flavorful it becomes.
In the morning, take the jar out of the fridge. Give it a good stir. The oats will have absorbed most of the liquid, creating a
thick, creamy, and spoonable consistency.