Heat the oil in a soup pot. Add the onion and sauté over medium heat for 5 minutes, or until translucent. Add the garlic, celery, and carrots and sauté for 3 to 4 minutes longer.
Add the water, potatoes, lentils, seasoning blend, paprika, and bay leaves. Bring to a slow boil, then cover and simmer until the lentils and vegetables are nearly done, about 30 minutes.
Add the tomatoes and parsley or cilantro, and simmer for 15 minutes longer over very low heat, or until some of the lentils are completely mushy, while others still hold their shape.
Season with salt and pepper. If time allows, this soup benefits from allowing it to stand for an hour or so before serving to develop flavor. Just before serving, add a little more chopped parsley or cilantro, then heat through as needed.