Pressure cook yellow lentils and soaked black chickpeas until soft.
Boil cubed yam with water, turmeric, and salt until tender.
Grind grated coconut and cumin seeds into a coarse paste.
Combine cooked lentils, chickpeas, and yam; stir in coconut paste and simmer for 5 minutes.
Heat coconut oil, crackle mustard seeds and curry leaves; temper the kootu and serve hot.