Pour 1/2 cup oats into 4, 8-ounce mason jars, then pour 1 teaspoon chia seeds into each jar.
Blend or whisk the milk, pumpkin puree, pumpkin spice, vanilla, and maple syrup until smooth, then pour an equal amount of the mixture (about 1/2 cup plus 1 tablespoon) into each jar.
Seal the jars, shake them, and then refrigerate overnight. When you're ready to eat them, sprinkle the pecans over top. These can be enjoyed hot or cold, depending on your preference.