Preheat the oven to 400 degrees and liberally spray a muffin tin with cooking spray. Set aside. Meanwhile in a large bowl add the baking mix. In a small bowl whisk together the milk egg, pumpkin, sugar, and melted butter. Pour the pumpkin mixture into the baking mix and stir until well combined. Stir in the nuts if you are using them. Portion the batter into the prepared muffin tin and bake for 15 minutes or until muffins are golden brown. While the muffins are still warm, roll each muffin in the melted butter, then combine the cinnamon and the sugar in a plastic bag and shake each muffin in the mixture to coat. Serve and enjoy!