Whisk together pumpkin puree, eggs, coconut milk, sweetener, pumpkin pie spice, vanilla, and salt until completely smooth.
Pour the custard mixture into a greased 7-inch round baking dish that fits inside your slow cooker.
Place the dish in the slow cooker and carefully pour water around it until the water comes halfway up the sides of the dish.
Cover and cook on low for 3 hours or until the custard is set but still slightly jiggly in the center.
Carefully remove the dish from the slow cooker, let cool for 15 minutes, then refrigerate for at least 2 hours before serving.