Render bacon in a large pot over medium heat until crisp. Remove bacon and set aside, leaving rendered fat in the pot.
Add onion, carrots, and celery to the pot and cook until softened, about 5-7 minutes.
Add lentils, chicken broth, diced tomatoes, tomato paste, thyme, and bay leaf. Bring to a boil, then reduce heat and simmer for 30-40 minutes, or until lentils are tender.
Remove bay leaf. Stir in cooked bacon. Season with salt and pepper to taste. Garnish with fresh rosemary or tarragon.