Finely chop the onion & garlic, then slice the celery. Cut the carrot into chunks.
Heat the oil in a large pan and soften the onion, celery and carrot. Add the garlic, cook for another minute.
Add the lentils, stir for a minute then pour in the stock. Add the bay leaf.
Bring to the boil then simmer for 30 minutes. Shred the ham into bits and add to the soup to warm through.
Finely chop the parsley, add it to the soup.
Stir in the vinegar. Taste the soup, adjust the seasoning.
Serve with a dollop of yogurt if you like