In a large pot, heat the olive oil over medium heat. Add the onion and garlic and cook until softened, about 5 minutes.
Stir in the ginger, curry powder, cumin, coriander, turmeric, and cinnamon and cook for another minute.
Add the vegetable broth, sweet potatoes, lentils, tomatoes, salt, and pepper. Bring to a boil, then reduce to a simmer and cook until the sweet potatoes are tender, about 20 minutes.
Serve hot with chopped cilantro, if desired.
Interesting Facts
The sweet potatoes and lentils in this soup provide a great source of plant-based protein and fiber.
The spices and herbs in this soup add a unique flavor to the soup.