Heat the oil or water in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and cook for 1 minute longer. Stir in the sweet potato, beans, tomatoes with their juices, cumin, coriander, paprika, vegetable broth, and salt and pepper to taste. Bring to a boil, then reduce the heat to medium and simmer until the vegetables ar