Prepare the Dry Base: In a medium mixing bowl, combine the rolled oats, chia seeds, ground cinnamon, fine sea salt, and a pinch of nutmeg. Stir with a fork to ensure the spices are evenly distributed throughout the oats.
Whisk the Liquids: In a separate small bowl or liquid measuring cup, pour in the soy milk, maple syrup, and vanilla extract. Whisk vigorously for about 30 seconds until the maple syrup is fully dissolved into the milk.
Combine and Hydrate: Pour the liquid mixture over the dry oat base. Stir thoroughly until every oat is moistened and no dry pockets remain. The mixture will seem thin at first.
Portion into Jars: Carefully divide the oat mixture evenly among the three 10-ounce jars. Leave a little space at the top for potential expansion or future toppings.
Seal and Chill: Secure the lids tightly on each jar. Transfer the jars to the refrigerator to chill for at least 8 hours, or up to 4 days, allowing the oats and chia seeds to absorb the liquid and soften.