Preheat the oven to fan 170 degrees C.
Heat a large ovenproof skillet until hot and drizzle with little oil. Add the mince and chopped green part of the leek, as well as diced carrot and parsnip. Cook for 5 minutes over a high heat, stirring the mince to break up.
Add the cornflour, followed by the stock and stir. Season with black pepper and few shakes of Worcestershire sauce. Cover, simmer gently for 15 minutes and then stir in the tinned lentils and cook for a few minutes, until warmed through.
In the meantime, in preparation for the topping, boil the potatoes in the skin for 12 minutes.
Heat a separate non stick pan and drizzle with oil. Add the grated carrots and stir fry for 3-4 minutes until softened.Remove into a mixing bowl.
Drain the potatoes and cover them with cold water, cooling for 2 minutes. Drain again and peel off the skins.Grate on a coarse grater and add to the carrots, using for to mix together.
Spoon the potato and carrot mixture on top of the mince and veg mix. Bake for 40 minutes or until the top of the pie is golden and crisp. Add grated cheese on top for the last 5 minutes of cooking. If you added the cheese straightaway, it would burn before the all topping is crispy. The time of cooking might depend on your individual oven. You might need to use the grill option to finish crisping up the topping of the pie.