Start by lightly spraying a 9-inch pie dish with non-stick cooking spray.

In a food processor, pulse the graham crackers until fine crumbs form, about 30 seconds. Add melted butter and sugar, pulse until resembling wet sand.

Press the crumb mixture into the bottom and sides of the prepared pie dish. Freeze for about 15 minutes to set.

In a mixing bowl, combine softened cream cheese and pumpkin puree. Mix on low speed until smooth and well combined.

Sprinkle in brown sugar, vanilla extract, and pumpkin pie spice. Mix on low speed until well incorporated.

Gently fold in 2 cups of whipped topping into the pumpkin mixture using a spatula.

Pour the pumpkin mousse filling into the chilled crust, spreading it evenly. Cover with plastic wrap and refrigerate for at least 6 hours or overnight.

Before serving, gently spread the remaining whipped topping over the mousse and dust with ground cinnamon if desired.

Slice the pie into wedges and serve chilled, optionally drizzling with caramel or serving with fresh berries.