Heat a 5 litre pot and add the olive oil, onions and bacon and stir till starting to get soft. Add the ginger, garlic and turmeric. Stir well and cook or 1 minute. Add the sweet potato, tomato passata and stock. Simmer till the potatoes are soft, 15 to 20 minutes.
Pour in the lentils water and all. Bring back to the boil.
Season with salt and pepper and stir in the parsley. Turn off and stir in the spinach if using.class