In a food processor, using the S-sharped blade whizz all the ingredients for the crust (dates, walnuts, coconut, cacao powder and the slat). You might have to start initially with pulse mode as the dates can be a bit tricky until they get going into the desired texture. When they are becoming a thick crumbed paste take out and put on a 23 cm (aprox. 9 inch) tray. Ideally would be a loose based baking tray but if you do not have one of those in this size, line any dish (that has got edges of at least 1 cm height that matches the given size) with a few layers of cling film or aluminium foil and leave some extra length to form some edges to make it easier to handle when you will need to take it out and transfer it onto the serving plate. Making use of your own fist and palm, spread the base mixture and press it evenly into the base pushing against the sides of the dish so that it forms the edges that should go up for 1 cm or almost.
Wash the food processor or wipe clean. Using the same S shaped blade, put all the filling ingredients in (the soaked cashew nuts, lime juice, the avocado flesh, mango, the melted coconut oil and the agave or date syrup), whizz them well until you get a nice and pretty smooth paste.
With the help of a spatula transfer the filling mixture on to the base and spread evenly, I will even allow you to give it a little shake if you wish ;-), just go for it.
Chill for about 3 hours in the fridge allowing to set beautifully. After chilling time decorate with some thinly cut lime slices as well as some lemon and lime zest.
Because the quantities are quite for some number you could easily freeze some by slicing it into desired sizes and it can be kept in the freezer for quite some time (up to 2 months). Whenever you wish to serve one or more, take out of the freezer and defrost for a minimum of 4-5 hours in the fridge where can be kept for as long as 6-7 days.