Pressure-cook the chickpeas and kale together until tender. If you don't have a pressure cooker, soak the chickpeas overnight and then place them in a pot with the kale (use fresh kale if you don't want to use the frozen). Cover with water and cook about 45 minutes to an hour or until the chickpeas are tender.
Heat the oil in a separate pot and add the cumin seeds.
When they sputter, add the onions and red chillies and saute until they start to brown, about 3-4 minutes.
Add the ginger and garlic and saute for a few more seconds.
Add the sambar powder, turmeric, and coriander powder. Mix well and then add the sweet potatoes.
Saute the sweet potatoes for five minutes or until they start to soften. Now add the chickpeas and kale and any stock from cooking the chickpeas, and bring to a boil. If the mixture is too dry, add water.
Cover the pot and cook for another 10 minutes or until the sweet potatoes are really tender.
Add the coconut milk and lemon juice. Stir well and turn off before the stew comes to a boil.
Serve hot over some rice or bulgur or couscous.