Finely chop the onion and garlic. Cut the potatoes, parsnips and carrots into bite-sized chunks.
Heat the oil in large pan and gently sauté the onion and garlic for about 5 minutes, then add the chopped vegetables and stir for a minute or so. Add the spices and stir to coat, then pour in the stock and passata.
Add the red lentils and bring to the boil. Cook over low heat for about 25 minutes, or until the vegetables are tender. Add more stock, if needed.
Scatter the chopped coriander on top just before serving.