Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the graham cracker crumbs and melted butter. Mix until well combined.
Press the crumb mixture into the bottom of a 9x13 inch baking dish to form a crust.
In another bowl, beat the cream cheese and powdered sugar together until smooth and creamy using an electric mixer.
Add in the pumpkin puree, vanilla extract, and pumpkin pie spice. Mix until fully combined.
Fold in the whipped topping gently until the mixture is smooth.
Spread the pumpkin mixture evenly over the graham cracker crust in the baking dish.
In a separate bowl, combine the sweetened condensed milk and cinnamon. Pour this over the pumpkin layer evenly.
Cover the dish and refrigerate for at least 4 hours or overnight for best results.
Serve chilled and garnish with additional whipped topping and a sprinkle of cinnamon if desired.