In a large soup pan, sauté onions in oil over medium heat until onions are translucent – about 8 minutes.
Add carrots, celery, and sweet potatoes, and continue sautéing for 6 to 8 minutes.
Stir in kale, parsley, and garlic. Sauté for 2 minutes or until kale is wilted and bright green.
Add water or broth and diced tomatoes. Turn heat to high.
Add seasonings and lentils, cover, and bring to boil.
Reduce heat and cook at a low boil for 45 minutes or until lentils are tender. Remove from heat and allow to sit (covered) for an additional 10 minutes to allow flavors to meld.
Notes
The amount of salt needed will depend on how much salt is in the diced tomatoes, broth, and tomato puree. If you use low-sodium version of these ingredients, you may want to increase the salt slightly.