There are many ways to make a great lentil soup, but this Greek version is a favorite because of its simplicity and zingy flavor. For a plant-based soup, you can't do much better than lentils.
Heat olive oil in a large pot over low heat. Add onions, celery, garlic, and a teaspoon of salt. Stir then cook for about 10 minutes, or until the vegetables have started to soften.
Add the vegetable broth to the pot. Stir in lentils, vinegar, tomato paste, and bay leaf. Bring to a boil then reduce heat and simmer for about 30 minutes or until the lentils are soft. Taste and adjust seasonings. Remove bay leaf.
Ladle into bowls and serve with a drizzle of olive oil and another splash of vinegar.