Warm the Pumpkin Milk. Combine half of the milk with the pumpkin purée, salt, and brown sugar in a small pot. Warm over low heat, stirring, just until the sugar dissolves and the mixture is smooth, then take it off the heat. If you're using uncooked pumpkin puree, bring it to a boil instead and remove it immediately.
½ cup milk, 3 tablespoons pumpkin purée, ⅛ teaspoon salt, 2 teaspoons brown sugar
Stir In Flavorings: Stir in the maple syrup, cinnamon, nutmeg, and the remaining cold milk, then carefully taste and add more spice or sweetener if needed — the mixture should be a bit sweeter than you'd like.
1 teaspoon maple syrup, ¼ teaspoon cinnamon, pinch nutmeg
Combine Oats: In a glass jar, combine the rolled oats and chia seeds.
½ cup rolled oats, ½ tablespoon chia seeds
Pour Over Oats: Pour the cooled pumpkin-milk mixture over the oats and chia, then stir well to combine.
Refrigerate 6+ Hours: Cover and chill the jar in the refrigerator for at least 6 hours, or overnight, so the oats soften and the flavors meld.
Serve: Give the oats a final stir and enjoy cold straight from the jar; add any toppings you like.