While the sweet potatoes are baking, get the curried chickpeas ready.
Heat oil in a pan over medium heat.
Add cumin seeds and allow them to sizzle.
Add chopped onion. Stir fry till they are soft.
Add garlic, ginger and green chilli pastes. Stir fry for a minute.
Add garam masala, coriander, cumin, turmeric and chilli powder. Mix well.
Add salt and the tomato puree. Mix well.
Add water. Cover the pan and allow the curry to cook over low heat for 5-10 minutes.
Remember to stir it in between so that the curry does not burn.
When the curry becomes thick, remove the pan from the heat. Keep it covered in the pan till required.