In a large kettle, heat olive oil over medium-high heat.
Add onions, celery, and carrots, sautéing for 5 minutes.
Add lentils, garlic, bay leaf, pepper, oregano, tomato paste, and 8 cups cold water (or enough to cover).
Bring to a boil.
Cover the kettle and simmer over low heat for 1 hour.
Add more water if the soup becomes too thick.
Add salt and vinegar to the lentil mixture, stir well, and cover.
Continue simmering, stirring occasionally, for an additional 30 minutes or until lentils are tender.
Stir in chopped parsley and serve the soup in individual bowls.
Notes / Tips / Wine Advice:
Wine Advice:Pair this hearty Greek Lentil Soup with a medium-bodied red wine like Xinomavro or a Cabernet Sauvignon. The wine's structure and fruitiness will complement the earthy flavors of the lentils and enhance the overall dining experience. Cheers!