Pre heat oven to 200c/180c Fan/Gas Mark 6.
Wash diced potatoes, add to a pan of boiling water with a large pinch of salt and simmer until soft.
Make up beef stock using 300ml boiling water and 2 stock cubes.
In a large pan, over a medium heat add boiling stock, peas, carrot, onion and red pepper. Allow to simmer covered for 5 - 6 minutes.
Add Garlic, Basil, Tomato Puree and Marmite. Allow to simmer uncovered for a further 2 - 3 minutes.
Add beef mince and continue to simmer uncovered for 10 minutes, stirring often. Keep simmering until most of the liquid has reduced and the mixture is a thick gravy like consitancy.
Line the bottom of a large oven proof dish with your mince mixture and set aside.
Drain potatoes, add yoghurt and a season with a good pinch of salt. Mash potatoes until creamy and fluffy. Add extra yoghurt if required. [Don't be worried if its a bit lumpy, you do not want the potatoes to be too runny]
Cover the mince mixture with potato and fluff with a fork. Garnish with tomato slices if required.
Place into the oven for 20 - 25 minutes or until crispy and golden.