Preheat the oven to 375°F (190°C) and grease an 8x8 inch baking dish with butter or non-stick spray.
In a large mixing bowl, whisk together the pumpkin puree, milk, eggs, maple syrup, and vanilla extract until smooth.
Add the rolled oats, baking powder, pumpkin pie spice, and salt to the wet mixture and stir until thoroughly combined.
Fold in half of the chopped nuts.
Pour the mixture into the prepared baking dish and spread into an even layer.
Sprinkle the remaining nuts over the top of the oats.
Bake for 35 to 40 minutes, or until the center is set and the edges are lightly golden brown.
Remove from the oven and let cool for 5 to 10 minutes before slicing and serving.