Heat the oil in a large pot and add the onion. Cook for 5 minutes until softened then add the garlic and cook for another couple of minutes. When everything is really soft add the spices and stir to coat.
Add the sweet potato, stock, chopped tomatoes and lentils to the pot and bring to a boil. Simmer for 20-30 minutes until the lentils are al dente and the sweet potato is cooked. Add the beans and serve.
Nutrition information is an estimate and will vary depending on the ingredients used.