Preheat the oven to 350°F.
Add the pumpkin puree, oat milk, brown sugar, agave, cornstarch, vanilla extract, pumpkin pie spice, cinnamon, and salt to a large mixing bowl.
Whisk everything together until the pumpkin filling is smooth and the cornstarch is completely mixed in with no visible lumps.
Pour the pumpkin mixture into the vegan pie crust and smooth out the top if needed.
Bake at 350°F for 1 hour.
Remove the pie from the oven and let it cool completely at room temperature.
Once the pie has cooled, place it in the refrigerator for at least 3 hours to finish setting.
Top with vegan whipped cream before slicing and serving.