Heat the olive oil in a large pan over medium heat. Add the cumin seeds and let them sizzle for 30 seconds. Then add the diced onions and cook for 4 to 5 minutes, stirring occasionally, until lightly golden.
Stir in the garlic and spices and let them cook for thirty seconds.
Add the beans, sweet potato, parsley stems, lemon zest and water. How much water you add will depend on the type of beans you use and the consistency you're after. Start with the smaller amount and add more if needed. Give everything a good stir, bring the mix to the boil, cover with a lid, turn down the heat and simmer for 10 to 15 minutes or until the sweet potato is tender. Stir occasionally to prevent the beans sticking to the bottom.
Stir in the tahini and simmer for a further minute.
Turn off the heat, add the lemon juice, salt and pepper, then give another good stir. Taste test and add more, salt, pepper or lemon juice if you think any of them are needed.
Scatter the parsley over the top and serve warm with crusty bread, rice or couscous. And maybe a side of greens or salad.
