Heat oil in 8 qut stock pot. Add the leeks and cook for 3 min.
Add the tomatoes and cook, breaking them up with a spoon, for 5 min.
Add the water and bring to a boil. Stir in the kale , sweet potatoes, lentils, thyme, salt, pepper, and basil (if using).
Simmer until the lentils are tender, about 30 min.
Spoon into individual bowls. Sprinkle with Parmesan (if using).