Preheat oven to 350°F. Lightly spray an 8x8 baking pan with oil (or line with parchment paper) and set aside.
In a food processor fitted with the S blade, pulse the pistachios until a flour like consistency.
Add flour, sugar and coconut oil, and pulse until combined and starting to form a dough. Do NOT over process!
Press dough into the bottom of your prepared 8x8 pan.
Bake crust for 20 minutes or until starting to brown and firm up. Set aside.
While your crust is baking, prepare the filling. Add tofu, avocado, powdered sugar, arrowroot powder, lime zest, lime juice and spinach (if using) in the food processor or blender. Process until completely pureed and smooth.
Pour the filling over the pre-baked crust and bake 20 minutes or until filing is set.
Transfer the baking dish to a wire rack to cool completely, about one hour. The filling will firm up as it cools.
Cut into squares and enjoy!