In a large soup pot or dutch oven, heat olive oil to medium heat.
Add leeks, onion, celery, carrot and swiss chard stems (if using) and cook for about 5 minutes until vegetables to begin to release their liquid.
Add herbs, garlic, salt and pepper and cook for another 1-2 minutes.
Add lentils, bay leaf and broth and tomatoes and bring to a simmer.
Cover and simmer for ~30-45 minutes, stirring occasionally and checking to see if more liquid is needed. If soup begins to get too thick, add water or more broth to thin it out.
When lentils are cooked and vegetables are soft, remove soup from heat and stir in the tea, sherry vinegar and parsley. Check for seasoning and add more salt and pepper if necessary.
Serve immediately, or refrigerate or freeze for later use.