From Wendy Hutton's Green Mangoes and Lemongrass - this is evidently a Vietnamese version of a common SE Asian dessert. Nonya cooks in Malaysia, for example, sometimes add diced sweet potato or yams to the basic mix (called Burbor Cha Cha, according to Wendy), and other cooks add jackfruit, young coconut etc. And I don't eat this with the banana's much either - I add fresh chopped mango to the sago mix: fridge-cold mango + warm sweet sago = delicious! There is an Indian mango, whose name escapes me but starts with 'b', which has a distinct (to me) kerosene-y aftertaste, and it is supurb with this.
Recipe posted by kgw