Combine the rolled oats, milk, Greek yogurt, brown sugar, chia seeds, vanilla extract, cinnamon, and salt in a 12-ounce glass mason jar.
Stir the mixture thoroughly with a spoon or seal the jar and shake vigorously until the brown sugar is fully incorporated and no dry pockets of oats remain.
Seal the jar with a tight-fitting lid and refrigerate for a minimum of 4 hours, though 8 hours is recommended for optimal texture.
Remove from the refrigerator and stir the oats once more to redistribute the moisture.
Thin with an additional splash of milk if a looser consistency is desired and serve chilled.