So I bought a packet of Lucuma powder from the health food shop to see what it was and what it tasted like.
Turns out it is dried powdered fruit. Native to the Andes, it has a sort of caramel/vanilla type of flavour.
It also turns out that Lucuma Ice Cream is one of the most popular flavours of ice cream in Peru. I have no idea what the real thing made from fresh fruit is like, but this recipe for a custard-based icecream flavoured with the powder is pretty good!