Set the cashews to soak overnight. The next day, rinse and set aside.
Rub two 6-inch tart pans with some melted coconut oil, and dust with cacao powder, or flour of your choice.
Make Base
Process the base ingredients until a sticky dough forms. Press it into each tart to form the crust. Put the pans in the freezer while you make the filling.
Make Filling
Process the filling ingredients until you have a pourable consistency. You can add a bit more lemon juice if your batter is too thick. Refrigerate leftover filling in a piping bag, ready to pipe rosettes when you are ready to eat.
Pour into each tart, and freeze them overnight. Thaw at least one hour to slice and serve. Top with rosettes (I didn't photography mine with rosettes!), fresh pitaya slices and lemon for presentation. Keep refrigerated.