In a medium saucepan, combine frozen blueberries and maple syrup. Cook over medium heat for about 10-20 minutes, stirring occasionally until saucy and chunky. Remove from heat and allow to cool.

In a large mixing bowl, combine the milk, Greek yogurt, rolled oats, chia seeds, remaining maple syrup, vanilla extract, a pinch of salt, and lemon zest. Stir until fully incorporated.

Cover the bowl tightly with plastic wrap or a lid and refrigerate for a minimum of 3 hours, or ideally overnight.

Divide the cooled blueberry sauce evenly among four serving jars. Layer the prepared overnight oats on top.

Garnish with fresh blueberries or extra lemon zest. Serve immediately or keep refrigerated.