Preheat oven to 350 degrees, and line a large baking sheet (with sides) with non-stick foil.
Place the graham crackers side by side on the baking sheet (you may need to break some of the graham crackers into smaller pieces to line the tray completely). Set aside.
In a medium sized saucepan, add in butter, pumpkin puree, brown sugar, pumpkin pie spice, and cinnamon.
Bring the mixture to a boil, whisking constantly. Once it has reached a boil, reduce the heat to med-low, whisking the mixture for another 3 minutes.
Remove from the heat and pour the mixture over the graham crackers. With a rubber spatula, spread the mixture over the graham crackers in an even layer.
Bake the graham crackers for 5-6 minutes, or until the liquid is bubbling.
Melt the chocolate in the microwave (in 30-second increments at 50% power, stirring after each hit) or over a double broiler. Pour the chocolate on top of the graham crackers, and spread it evenly over the grahams.
Top with chopped pecans, if desired.
Allow the toffee to cool before breaking or cutting into pieces (it takes about 3 hours cooling on the counter and about 1 hour in the fridge).
Enjoy!
(Leftovers can be stored at room temperature or in the fridge.)