Wash and halve the tomatoes. Wash the chillies, halve, deseed and cut into fine strips. Peel and finely slice the garlic.
Finely chop the peanuts, and place with the tomatoes, chillies, garlic, fish sauce, lime juice, sugar and lime zest in a bowl. Stir and set aside.
Peel the papaya then use a mandolin or vegetable peeler to cut the flesh into very thin slices.
Cut into fine strips with a knife.
Add the papaya to the marinade, mix well and season to taste. Toast the cashew nuts in a dry pan until lightly browned. Remove and allow to cool. Place the papaya salad in bowls and serve sprinkled with cashews.