1. Sort lentils and discard debris. Rinse lentils and put in a 6- to 8-quart pan. Add 4 cups water, broth, cumin seed, olive oil, cabbage, kale, carrots and tomatoes.
2. Bring to a boil over high heat, then cover and simmer gently, stirring occasionally, until vegetables are soft and flavors well blended, about 1 hour.
3.Trim ends from onions and chop onions. Ladle soup into bowls, add onions, and season to taste with salt.