1. Prepare the pie base by crushing the biscuits in a food processor, then microwave the butter until it is liquid and add to the crumbs, blending to combine.
2. Pour mixture into the dish and press with fingers to form a crust. Set aside in the fridge to cool and solidify.
3. Prepare the filling by adding to a blender the juice and zest of the lemon, plus the juice and zest of one lime, the condensed milk and lastly - to prevent any oxidisation of the avocado - the avocado pieces.
4. Blend until smooth and even.
5. Cover base with the cream and refrigerate for 2 hours.
6. Decorate with the zest of the remaining lime.