Preheat the oven to 400 degrees F (200 degrees C). Grease a 10x15 inch jellyroll pan.
Arrange cinnamon graham crackers with sides touching in a single layer to cover the bottom of the pan. Sprinkle the walnuts evenly over the crackers. In a small saucepan over medium heat, combine the brown sugar, butter and cinnamon. Cook stirring constantly until the mixture begins to boil. Continue to boil the syrup for 3 minutes without stirring. Remove from heat and pour over crackers.
Bake for 8 to 10 minutes in the preheated oven, until bubbly and slightly darker around the edges. Cool completely in the pan. Break into pieces and store in an airtight container at room temperature.