1. Wash lentils thoroughly. Bring a pan of water to the boil, add lentils and cook for 10 minutes. Peel the onions, then chop 1 onion and add to the pan with bay leaves. Bring to the boil, then cover, reduce the heat and simmer for 20 minutes, until the lentils are soft. Drain, then discard the bay leaves.
2. Prepare the remaining vegetables. Peel the turnip and parsnip. Wash and trim the leeks, then slice. Dice the turnips, remaining onions, parsnips and carrot.
3. Pierce each of the tomatoes with a knife, then place in a bowl and cover with boiling water. Leave to soak for 5 minutes. Peel the tomatoes (the skins will come off easily), chop and reserve.
4. Trim the bacon, discarding the rind. Cut into small pieces. Heat oil in a heavy-based pan and sauté the onions until tender, with the bacon.
5. Add the carrot, turnips and parsnips to onions and cook for a further 5 minutes.
6. Add stock, then grate orange rind into pan. Squeeze juice from orange and add to vegetables. Blend tomato purée with 30 ml water and stir. Bring contents of pan to the boil, then cover, reduce the heat and allow the soup to simmer for 25 to 30 minutes, until the vegetables are soft.
Add the tomatoes and lentils to the pan. Season and continue cooking for a further 10 minutes. Sprinkle with parsley and serve immediately.