1. In a 2-gallon pot over medium-high heat add lentils, stock, onions, carrots, celery, fennel and garlic and begin to simmer for 35-40 minutes until lentils are tender. Add more liquid if needed to finish cooking lentils.
2. Remove half of the soup and blend until smooth. Pour the puree back into the soup and turn heat to low just while folding in remaining ingredients. Remove from heat and allow greens to wilt into the soup.