To make the sweet potato gravy, heat a dash of oil in a large, deep saucepan. Add the diced onion, sweet potato and pepper, and cook over a medium heat for a few minutes, until the onion is soft and translucent. Add the tin of chopped tomatoes, vegetable stock, and some black pepper, along with the spices. Bring to a simmer, and cook until the sweet potato is very soft - at least 20 minutes.
When the vegetables are very soft, use a hand blender to blend the sauce until smooth. At this point, you can add a dash more water if needed, until the sauce reaches your desired consistency.
To make the chickpea dumplings, combine the suet, chickpea flour and plain flour in a bowl, along with the chopped herbs and a generous pinch of salt and pepper. Add enough water to bring the mixture together into a sticky dough (stir with a spoon, as it will just stick to your hands) - I used about 175ml.
Add the dumpling mixture to the sweet potato gravy in tablespoon-sized dollops - I ended up with 12 dumplings in total. Don't worry if they drop down into the gravy. Cover the pan, and cook gently for a further 15-20 minutes, until the dumplings are firm.