Preheat oven to 350 degrees. Coat a 6-cup donut pan with cooking spray. Using a hand mixer, beat oil and brown sugar on low. Add one egg at a time, then pumpkin puree until incorporated. Add flour, salt, pumpkin pie spice and baking powder and beat on low until incorporated, scraping the sides of the bowl as needed. Transfer batter to a large Ziploc bag and seal to close. Snip one of the bottom corners of the bag with scissors to create a piping bag. Pipe batter into each well of the donut pan until almost full. Tap the pan on the counter to evenly distribute batter. Bake 15 minutes, until set. Repeat steps for another batch. In a small bowl, mix together sugar and cinnamon. Place donuts in a large Ziploc bag with the cinnamon sugar mixture and toss to combine.