Preheat oven to 375°F. Spray a 12-inch cast iron skillet or a 9x13 dish with coconut oil spray. Set aside.
In a large bowl, whisk together pumpkin, sweetener, eggs, pumpkin pie spice, salt, and vanilla extract.
Whisk in heavy cream until smooth.
Pour into prepared skillet and set aside.
In a medium bowl, whisk together flours, sweetener, cinnamon,nuts and salt. Add melted butter and stir with a fork until crumbly. (Can also beat with a hand mixer until crumbly if needed).
Spread cinnamon streusel topping on top of pumpkin pie mixture in an even layer.
Bake until the filling is set and the top is golden brown, 40 to 45 minutes.