Preheat the oven to 350°F. Grease a 9-inch springform pan; set aside.
Pour chocolate chips into a microwave-safe bowl and microwave for 30 seconds. GIve the chocolate chips a quick stir, then microwave another 30 seconds. Stir again and continue until the chocolate chips are melted. Set aside.
For the brownie layer:
In a large mixing bowl, stir together 1 cup pumpkin, 3/4 cup sugar, vegetable oil, and vanilla extract.
To this mixture, stir in the flour, cocoa powder, 1 tablespoon tapioca flour, baking soda, and salt.
Add the melted chocolate and continue stirring until fully combined.
Pour the brownie mixture into the prepared pan, using a spatula to spread the batter all the way to the edges of the pan. Wipe out the bowl and move on to the pumpkin layer.
For the pumpkin layer:
Into the mixing bowl, add the remaining 3/4 cup pumpkin, 1/3 cup sugar, oat milk, 2 tablespoons tapioca flour, 1 teaspoon vanilla extract, ginger, cinnamon, nutmeg, and allspice. Stir until thoroughly combined.
Into the baking pan, pour the pumpkin over the brownie layer. Use a spatula to spread the pumpkin mixture so that it covers the brownie layer completely.
Bake for 35 minutes, until the pumpkin layer is somewhat firm, with very little jiggle to it.
Set the pie on a cooling rack for 30 minutes then transfer to the refrigerator. Allow to set for at least 2 hours then slice into wedges and serve.