Preheat the oven to 350 degrees F. Line a 9×13-inch rimmed sheet pan with parchment paper. Set aside.
Scoop the pumpkin seeds out of the pumpkin and into a large collander. Rinse the pumpkin seeds thoroughly under cold running water. Use your hands to separate any lingering pumpkin flesh from the seeds. Shake off as much water as you can, then pat dry with paper towel.
Stir together the melted butter, brown sugar, cinnamon and salt in a medium mixing bowl, until completely combined. Add the pumpkin seeds and toss to coat. Evenly spread the pumpkin seeds in a single layer on the prepared pan.
Bake for 25-30 minutes, stirring/flipping once or twice, until the seeds are golden and crispy.