Pre-heat oven to 350 degrees and line a 9x13 baking pan with foil so it's overhanging on all sides.
In a medium bowl, mix together flour, ¼ cup granulated sugar, all the brown sugar, and cinnamon. Using a pastry cutter, fork, or your fingers, cut in butter until the mixture resembles coarse crumbs. Stir in oats and walnuts or pecans.
Set aside 1 cup of the mixture and place the rest in the prepared baking pan. Using your fingers, press the mixture into an even layer on the bottom of the pan. Bake for 15 minutes. Remove from oven, but keep oven on.
While crust is baking, make filling. In the bowl of a stand mixer or in a large bowl with a hand mixer, beat cream cheese for about 2 minutes, until smooth. Add remaining granulated sugar, pumpkin, eggs, vanilla, pumpkin spice, and salt to bowl and beat until smooth and combined.
Pour the pumpkin mixture over the top of the baked crust. Sprinkle with the remainder oat mixture and butterscotch chips.
Bake for another 25 minutes until filling is just set. Let cool completely before slicing.
Store in airtight containers in fridge.