To a large mixing bowl, add your plain Greek yogurt, sugar-free pudding mix, vanilla, pumpkin pie spice, and pumpkin puree.
If using an electric mixer, mix until all ingredients are thoroughly combined and smooth, incorporating air to create a fluffy texture. If using a whisk, follow the same steps.
Dish the Greek yogurt mousse mixture into a small ramekin or decorative bowl and refrigerate for 2 hours, or until the mousse is set and the pudding mixture thickens.
Top the mousse with sugar-free whipped topping, sprinkle with cinnamon, and enjoy after your Thanksgiving dinner.