Add oats, raisins and pumpkin pie spice to a blender and then pour in milk, adding more to cover the oats if needed. Stir completely and set aside until the oats are soft, 15 minutes.
Blend on high speed until pureed and smooth, about 1 minute. Add yogurt, brown sugar and 1 cup ice, and blend on high speed until smooth, about 30 seconds. Pour into glasses.