Chop the ginger and garlic and fry in hot oil. Cut the chicken fillet into small pieces and add to the pan. Add the curry paste. Cut the mangoes and spring onions into small pieces and add to the chicken with the lemongrass and snow peas. Add coconut milk and the cane sugar, bring to the boil briefly and then cover and cook over medium heat for about 30 minutes. Add cashew nuts after about 20 minutes of cooking.