In a small saucepan, combine the blueberries. maple syrup, cornstarch, lemon juice, and water (if using).
Bring to a boil over medium heat. Reduce heat to low and simmer for 5 minutes until thickened, stirring occasionally. Set aside to cool to room temperature (you can transfer the pot to the fridge for a few minutes to speed this up).
In a large bowl, whisk together the yogurt, milk, maple syrup, and vanilla.
Stir in the oats, salt, and cinnamon. Let the mixture sit for 10-15 minutes to thicken slightly.
Spoon the oats into half pint (250 ml) containers or jars, alternating with the blueberries.
Place lids on the jars or containers and refrigerate overnight, or up to 4 days before enjoying. Serve topped with fresh blueberries, bananas or other berries, if desired.