Cook and stir olive oil, onion, carrots, parsnips, beet, rutabaga, and fennel in a soup pot over medium heat until vegetables begin to soften, about five minutes.
Mix vegetable broth into vegetables and bring to a boil.
Add lentils, dried thyme, bay leaves, and parsley. Reduce heat to low and simmer until lentils are tender, about 35 minutes. Season with salt and ground black pepper to taste.