Fry the garlic, spices and chopped ginger in hot oil for 3-4 minutes until everything is soft but not brown. Boil the potatoes for 5 minutes, cut into cubes. Add to the spices with vegetables and peppers. Fry for 7-10 minutes, stirring occasionally. Add coconut milk and tomatoes. Season to taste, simmer for 15-20 minutes. Add the cashew nuts to the vegetables, arrange on a plate in a bed of rice. Garnish with the coriander sprig and serve with yoghurt.