In a large saucepan over medium heat, sweat the onion, carrot and celery in oil for about 5 minutes, or until onion is translucent and vegetables brighten in color.
Add tomatoes (squeezing to break up if whole), broth and lentils. Bring to a boil over high heat, stirring occasionally. Reduce to a simmer.
Cook until carrots are just tender if planning to leave the vegetables whole. If planning to puree, cover and cook for 30 minutes, until all vegetables are very soft. Stir occasionally to keep lentils from sticking to the bottom of the pot.
Leave soup chunky, or puree in batches in a regular blender or food processor, or with an immersion blender.
Package in one-cup portions in containers or zip-closure freezer bags. Freeze for up to 6 months.
To serve, heat and garnish as desired. Please see full blog posting for suggestions.