Preheat your oven to 350°F (175°C) and grease your donut pan.
In a large mixing bowl, combine the pumpkin puree, brown sugar, eggs, and vegetable oil. Whisk until smooth.
In another bowl, mix together the flour, baking powder, cinnamon, and salt.
Gradually add the dry mixture to the wet mixture and stir until just combined.
Transfer the batter to a piping bag and fill each donut cavity about ¾ full.
Bake for 12-15 minutes or until a toothpick comes out clean.
Allow the donuts to cool for 5 minutes in the pan, then transfer to a wire rack.
While cooling, mix granulated sugar and cinnamon; roll each donut in the mixture until coated.