Combine the base. In a jar or bowl, add oats, milk, yogurt, pumpkin puree, maple syrup, chia seeds (if using), vanilla, pumpkin spice, and a pinch of salt.
Stir well. Mix until everything is evenly combined and no pockets of pumpkin or spice remain. If it seems very thick, add a splash more milk.
Chill overnight. Cover and refrigerate for at least 4 hours, ideally 8–12. The oats and chia will soften and thicken as they soak.
Adjust texture. In the morning, give it a stir.
Add a little milk if you want it looser, or a spoon of yogurt for extra creaminess.
Top and enjoy. Add nuts, seeds, fruit, or a drizzle of maple syrup. Eat cold, or warm gently in the microwave for 30–45 seconds if you prefer it cozy.