Crush the graham crackers and mix in a bowl with the butter and sugar until combined well.
Press the crust mixture into a 9 x 13″ cake pan until firmly in place. Bake for 5 minutes, and then remove from the oven.
While the crust is baking for 5 minutes, mix together the filling ingredients: pumpkin, sweetened condensed milk, eggs, cinnamon, pumpkin pie spice, and salt until smooth.
Pour the filling mixture over the crust.
In a small bowl, mix together the flour, sugars, and cinnamon for the streusel. Pour in the butter and water, stirring to combine. It will resemble a dry cookie batter.
Spoon the streusel topping over filling in an even layer. DO NOT press it down.
Bake at 425 degrees for 15 minutes. Then, without removing the bars from the oven, reduce the heat to 350 degrees and bake for an additional 25-30 minutes or until the bars do not wobble when you shake the pan. Remove from the oven and cool completely before cutting.