Preheat the oven to 350 degrees F.
Spray a 9x9 inch square baking dish with cooking spray, set aside.
In a large bowl, whisk together the oats, brown sugar, cinnamon, nutmeg, baking powder and salt.
In a medium bowl, whisk together the milk, melted butter, eggs and vanilla extract.
Pour the wet mixture into the dry mixture and stir to combine.
Stir in the blueberries.
Spread evenly into the prepared pan.
Top with chopped nuts, if desired.
Bake for 35-40 minutes or until center looks almost set.
Serve immediately with yogurt, fresh berries, syrup or honey if desired.
Store leftovers in the refrigerator.