Chill the Can: Make sure your can of full-fat coconut milk has been refrigerated for at least 8 hours, or preferably overnight. Do not shake the can.
Scoop the Cream: Carefully open the can and scoop only the thick, solid white cream from the top into a medium mixing bowl. Reserve the leftover clear coconut water for another use (like a smoothie).
Combine Ingredients (One-Bowl Method): To the same bowl with the coconut cream, add the pumpkin puree, granulated sweetener, pumpkin pie spice, vanilla extract, and pinch of salt.
Whip the Mousse: Using an electric hand mixer, whip all the ingredients on medium-high speed for 30-60 seconds, or until the mousse is light, fluffy, and completely smooth.
Taste and Adjust: Taste the mousse. Add a little more sweetener or spice if desired and briefly whip again to combine.
Serve: Divide the mousse between two small ramekins or jars. You can spoon it in or pipe it for a cleaner look. Top with optional chopped nuts, a dollop of whipped cream, and a final dash of cinnamon. Serve chilled.