Heat non-stick saute pan or medium sized saucepan with vegetable oil till medium hot.Place potatoes in saucepan with water. Boil for 10-12 minutes or until soft. Time depends on how large you chopped potatoes. Drain and leave to steam dry in a colander.
Saute the onions till lightly brown. Add garlic and saute for a few minutes. If pan too hot turn down a little to prevent garlic burning. Stir frequently.
Add another teaspoon of oil if required to prevent sticking. If cutting down on oil a few tbsp of water could be added.
Add Quorn or half the bag depending on how many servings you want. An average sized bag tends to feed 4 and the family sized pack could feed 6. Alternatively add the lentils.Saute for 5 minutes. Stir frequently.
Add tomato puree and cook for a few minutes.
Add cooked carrots and celery. Stir.
Add chopped tomatoes. Mix.
Add about 250-300 ml of carrot-celery stock and bring to boil.
Gently simmer for about 20 minutes, if there doesn't seem to be much stock then add some more, you don't want it too liquidly though. But you don't want it too dry either. if you run out of stock you can use boiling water.
Preheat oven to 180 fan /200 celsius/Gas mark 6/400 Fahrenheit
While mince is cooking, transfer potatoes to a bowl and add the margarine, milk and season to taste. Mash till smooth. Set aside till required.
Prepare a medium-large pyrex or baking dish. Or individual single potion dishes. Check mince mix is seasoned to taste. Spoon into the baking dish/es. If you want to up the veg content add a handful of frozen peas/sweetcorn and mix. Alternatively a tin of baked beans is quite a delicious addition! And counts as a portion of vegetables!
Scoop ladlefuls of mashed potatoes over the mince. Spread out evenly over mince. Use a fork to create a swirly, peaked pattern on top.
Bake for about 20 minutes on the middle rack of oven. Until potatoes start to look brown or crispy. This will depend on your oven and how hot it runs.
Carefully remove from oven and sprinkle the cheese on top. Place back in oven.When cheese melted, golden brown and looking crispy, about 10-15 minutes, remove from oven. Its ready to serve.
Can be cooled and kept for about 3 days. Can be prepared in advance, cooled and frozen. Defrost and reheat for 45 minutes before serving. (Check the pie after 30 minutes and if its getting too dark then you can cover with a layer of tin foil.) At 180 Celsius/160 Fan/ Gas 4/ 350 Fahrenheit. Make sure the shepherds pie is piping hot when it comes out the oven.