This is a really good recipe for using up vegetables. The essential ingredients are the sweet potato, lentils and the spices; other than this you can put in just about anything, I have listed below the ingredients which I would normally use. If you are vegan make sure that your ketchup is dairy free. This is an optional ingredient anyway and is designed to add a little sweetness, you can use a pinch of sugar instead or a packet of instant tomato soup, or just leave it out altogether. The recipe works best in a slow cooker or oven-cooked in a casserole, but can also be cooked on top of the stove. If you find that it comes out watery, just add more lentils and cook down.