Line a 9x5-inch loaf pan with plastic wrap, overlaping all of the edges.
In a medium mixing bowl, stir together 1/2 cup whipped topping, pumpkin, sugar, and 1 teaspoon pumpkin pie spice. Set aside.
Arrange approximately four and a half graham cracker squares in the bottom of the lined pan. Break crackers as needed to fit in the pan.
Spread half of the pumpkin mixture over the graham cracker layer in the pan.
Place 1 cup whipped topping over the pumpkin mixture.
Top with approximately four and a half graham cracker squares, again breaking the crackers as needed to fit in the pan.
Spread the remaining pumpkin mixture over the graham crackers.
Top with remaining graham cracker squares, again breaking the crackers as needed to fit in the pan.
Spread remaining whipped topping over the graham crackers.
Cover loosely and refrigerate for at least 4 hours (up to overnight) to soften graham crackers.
Freeze cake for an hour to an hour and a half before serving to firm it up enough to slice. Remove from freezer and uncover. Lift cake from pan (using the overlap to pull up and out). Place on a serving plate and discard plastic wrap.
Dust cake with remaining 1/4 teaspoon pumpkin pie spice and cut into 9 equal-sized slices.
Serve immediately, garnishing with chopped walnuts (optional).
Notes
Serving size: 1 slice, approximately 1-inch thick.SmartPoints: 6 per slice (Green, Blue, and Purple). Walnuts are not included in the point values.