Preheat oven to 400ºF. Grease or line a 12-cup muffin pan.
In a small bowl, pour ½ cup milk over oats. Set aside for 10 minutes.
In a medium bowl mix flour, baking soda, baking powder, Pumpkin Pie Spice Mix and salt.
In a large bowl combine squash purée, egg, brown sugar and maple syrup. Mix well.
Stir in oat mixture. Add dry ingredients along with butter and 2 Tbsp remaining milk, stirring, until fully combined. Fold in raisins and walnuts.
Divide batter evenly between 12 muffin cups. Bake for 16-22 minutes until golden and a toothpick comes out clean.