Line a square baking dish with parchment paper. Then in a blender or food processor, process the walnuts until fully ground.
Next, add the dates, cocoa powder (1 tbsp) , and coconut to the walnuts and process until you get a slightly sticky result. Transfer this to the prepared baking pan, pressing the mixture in place to form a crust.
In your food processor or blender, place soaked and drained cashews, liquid stevia, vanilla extract, melted coconut oil, canned coconut milk, and remaining cocoa powder. Pulse the ingredients until completely smooth.
Transfer the ingredients to baking pan, evenly distributing it over the crust that you just made. Then, place the baking pan in your refrigerator until the ingredients are set, about three hours.
To make the topping, start by evenly distributing the pistachios on a on a rimmed baking sheet lined with a mat or parchment paper.
Next, combine together the brown sugar and water over medium heat, stirring as needed as the mixture turns brown and thickens. When you notice bubbles forming, wait about a minute and then remove the mixture from the heat and pour it over the pistachios. Once the pistachio and sugar have hardened you can break up the ingredients to use it as a topping over the cheesecake bars before serving.