Preheat the oven to 180 degrees c / 350 degrees F. Line a 1kg/2lb loaf tin with greaseproof paper.
Place the chopped onion, garlic, leek, celery and lentils in a large pot with the stock. Bring to the boil then cook for about 25 - 30 minutes until the lentils are soft.
Add all the other ingredients and stir together.
Spoon into the loaf tin. Place in the oven and cook for a further 30 - 40 minutes. Check after 30/25 minutes - if the top looks as though it's burning, place some greaseproof paper on it.
Once cooked, remove the loaf tin from the oven and leave to cool for five minutes. Turn out onto a warmed plate, then cut and serve. I've served it here with roast potatoes, red cabbage, carrots and broccoli.