Combine old-fashioned oats, chia seeds, Greek yogurt, milk, and cinnamon in a large bowl and stir to combine.
Layer oat mixture in two 8 oz. mason jars, alternating with cranberry sauce. I recommend 3 Tbsp oats, 2 Tbsp cranberry sauce, 3 Tbsp oats, 2 Tbsp cranberry sauce, and then topping each jar with remaining oats mixture.
Refrigerate overnight, or for at least 8 hours.