In a large pot, combine the broth, lentils, carrots, onions, celery, and bay leaves; bring to a boil. Reduce the heat, and simmer, covered, stirring occasionally, until the lentils and vegetables are tender (about 30 minutes).
Add the tomatoes (with juice), vinegar and pepper. Add the water (amount depending on how much soupy broth you desire). Cover and cook, stirring occasionally, until the flavors have blended, 10 minutes.
Sprinkle individual servings with chives, if desired.
Notes
If you are preparing this recipe as GLUTEN FREE, just be sure to use a brand of beef broth that is known to be GF.