In a large bowl, combine the oats, milk, eggs, walnuts, syrup, butter, banana, cinnamon, vanilla, baking powder, salt, and nutmeg. Carefully fold in 1 ½ cups of blueberries.
3 cups old-fashioned rolled oats, 1 ¾ cup milk, 2 large eggs, ½ cup walnuts, ⅓ cup maple syrup, ⅓ cup banana, ¼ cup unsalted butter, 2 teaspoons ground cinnamon, 2 teaspoons vanilla extract, 1 teaspoon baking powder, ½ teaspoon salt, ¼ teaspoon ground nutmeg