In a large bowl or an airtight container, combine the milk, pumpkin puree, pumpkin pie spice, and vanilla extract.
Add chia seeds and stir well. Let it sit for 5 minutes or so and give it another stir (the mixture will be liquid-y). Close the lid and refrigerate for at least 2 hours, preferably overnight. You can also divide the mixture into two small containers or mason jars.
When ready to eat, enjoy cold with your favorite toppings.
Notes
Prefer a thicker pudding? Add a bit more chia seeds (1 teaspoons at a time) and refrigerate for an additional 30 minutes.