Start by sautéing the onion and garlic and if you want to keep this oil free you can try water sautéing them. Once the onions are browned you can add the chopped tomatoes and spices, cook this until the tomatoes are completely broken down and almost turned into a paste.

Now add the remaining ingredients and cover with water (if you're using baby spinach add this at the end). Let it simmer till the sweet potatoes are done and until you reached your favorite consistency. If you'd like more sauce you can add water and if you'd like it to be thicker you can break down some of the sweet potatoes. Enjoy over rice or with roti, or whichever way you prefer.