Preheat the oven to 375 degrees. Line a 13 x 9 baking dish with parchment paper.
In a large bowl, combine the coconut, graham crackers, walnuts, and melted butter. Stir to combine.
Press the mixture into the bottom of the prepared dish.
In another bowl, mix the pumpkin, condensed milk, eggs, pumpkin pie spice and salt.
Spoon the mixture over the coconut mixture and smooth until even.
Bake for 30 to 35 minutes, until a toothpick comes out clean.
Allow to cool completely before frosting.
Frosting
Beat the cream cheese and butter together in the bowl of a stand mixer fitted with the paddle attachment on medium-high speed for 2 minutes.
Add the sugar, vanilla, and half and half, and salt. Start on low, and then increase to medium, beating for a total of 3 minutes. Scrape the sides as necessary. Turn the speed up to high and beat for 1 more minute.
Spread the frosting over the pumpkin bars and cut to serve. Alternatively, you can cut the bars and frost individually.