Start by preheating your oven to 185ºC (365ºF). Spray a 9" x 13" baking dish with cooking spray or line with parchment paper.
In a large mixing bowl, whisk together the pumpkin puree, melted butter, egg, vanilla extract and milk.
Then add your sourdough starter and whisk this until the mixture is smooth.
Now add in the brown sugar, rolled oats, baking powder, salt and pumpkin pie spice and stir together until all of the rolled oats are wet and everything is well combined.
Pour the oatmeal mixture into the pan you prepared and place into the oven for 45 minutes at 185ºC (365ºF).
Once the top is golden and the edges are starting to crisp, remove from the oven and allow to cool in the pan for around 10 minutes.
Cream Cheese Glaze
To make the glaze, melt the cream cheese in the microwave (I place it into the microwave for 1 minute, but adjust this depending on your own microwave).
Add the melted cream cheese, powdered sugar, maple syrup, milk and vanilla paste to a bowl and whisk together to create a drizzly glaze.
Drizzle the glaze over the warm sourdough pumpkin pie baked oatmeal.