Mash the chilli, garlic and sugar to a paste using a pestle and mortar or small processor. Stir in the lime juice and fish sauce, then set aside.
Peel, quarter, core and slice the pineapple at an angle. Toss with beansprouts, prawns, avocado, cucumber and tomato and some of the dressing. Pile into bowls and scatter with mint and cashews. Drizzle with the rest of the dressing and serve.