Prepare the Dry Base: In a large mixing bowl, add the rolled oats, chia seeds, cinnamon, ginger, nutmeg, and cardamom. Whisk everything together until the spices are evenly distributed.
Blend the Pumpkin Cream: In a separate medium bowl, combine the Greek yogurt, pumpkin purée, oat milk, maple syrup, monk fruit sweetener, and vanilla extract. Whisk vigorously until the mixture is smooth, creamy, and uniform in color.
Combine: Pour the liquid pumpkin cream mixture over the dry oat base in the large bowl.
Incorporate Thoroughly: Using a silicone spatula, fold the ingredients together. Scrape the sides and bottom of the bowl to ensure no dry pockets of oats remain and the mixture is fully combined.
Portion and Seal: Carefully divide the oat mixture evenly among the three jars. Seal each jar securely with its lid.
Chill and Set: Transfer the sealed jars to the refrigerator. Allow them to chill for a minimum of 6 hours, or overnight, until the oats have absorbed the liquid and the mixture has thickened to a spoonable, pudding-like consistency. Serve chilled.