Place the blueberries, banana, yogurt, milk, 3 tablespoons of walnuts, honey and vanilla in a blender. Blend until smooth.
Pour the blueberry-walnut mixture into a bowl and stir in the oats and chia seeds.
Pour the mixture into a jar or small serving container, top with remaining 1 tablespoon walnuts, cover, and refrigerate for at least 4 hours or overnight. Serve cold straight from the refrigerator.
