Heat oil in a large frying pan; cook onion and garlic, stirring, until onion is soft. Add spices; cook, stirring, until fragrant. Add potato; cook, stirring, until browned slightly. Stir in undrained crushed tomatoes, paste, sugar and the water; simmer, covered, about 25 mins or until potatoes are tender. Add chickpeas and coriander leaves; cook, stirring gently, until hot.