Add all of the above ingredients, except lentils, to the slow cooker, stir to combine. Cover and cook on low 8 to 10 hours. Add lentils the last hour of cooking time. Feel free to add or substitute your favorite vegetables.
Tip: Adjust the liquid for less or more thickness. First, try adding 1 cup each tomato juice and 1 cup vegetable broth. Remember, the slow cooker does not allow for much evaporation, so the amount of liquid you add initially will be about the same toward the end of the cooking cycle. It's easier to add liquid than to remove it. We like ours fairly juicy so we add the full amount and sometimes even more.