| *Preheat the oven to 200°C/Fan 180°C/Gas 6. You will need a buttered ovenproof dish, about 28x23x5cm (11x9x2in).
1. Cook the onions and garlic in the oil over a low heat in a large pan for about 10 minutes, or until soft. Add the celery and carrots, and cook for a further 5 minutes. Stir in the lentils, then add the chopped tomatoes, stock, tomato paste, sundried tomatoes and plenty of seasoning.
Bring to the boil, cover and simmer for about 20 minutes, or until the vegatables are tender. Check the seasoning.
2. Meanwhile, cook the potatoes in boiling salted water until tender.
3. While the potatoes are cooking, heat the milk and spring onions together in a small pan and simmer gently for about 5 minutes, or until the spring onions are soft. Drain the potatoes well, then add the warm milk with the spring onions, and the butter. Mash together, adding plenty of seasoning. Stir in two-thirds of the grated cheese and check the seasoning.
4. Spoon the vegetable mixture into the prepared dish and gently spread the potato on top. Scatter on the remaining cheese.
5. Cook in the preheated oven for about 30 minutes, or until the potato is golden and the sauce bubbling.