Preheat the oven to 350 degrees F. Grease a 9x13 inch baking dish, or line with parchment paper for easy removal later.
In a large bowl, whisk the flour, sugar and salt. Now add the softened vegan butter and stir with a large wooden spoon, or use an electric mixer, until combined. The mixture will be quite crumbly.
Set aside 1 cup of the mixture for topping the pumpkin bars. Press the rest of the mixture evenly into the baking pan and set aside while you make the pumpkin filling.
Make the pumpkin filling - To a blender, add all the ingredients for the pumpkin layer and blend until very smooth. Alternatively, simple whisk in a bowl until smooth, but make sure your coconut is smooth or it won't incorporate well (you can warm it in the microwave if it's chunky).
Pour the pumpkin filling over the crust in the pan, then sprinkle the crumbs you had set aside over the top of the pumpkin.
Bake in the oven for 35-40 minutes, until golden brown and mostly set on top. It might still look a bit jiggly; that's okay, it will firm up as it cools.
Let cool at room temperature for 30 minutes, then transfer to the refrigerator to chill for at least 2 hours.
Once chilled and firm, cut into bars and serve with vegan whipped cream or vanilla ice cream, if desired.