1. Heat a splash of oil in a large saucepan and cook the onion and garlic for 5 minutes until softened. Add the lamb and cook for a further 4-5 minutes until browned. Chop 1 of the tomatoes, stir into the lamb and onion mixture and cook for 2 minutes until pulpy. Add the stock pot, dried herbs and 400ml boiling water. Bring to the boil and simmer for 20 minutes.
2. Meanwhile, preheat the oven to 220ºC, gas mark 7. Place the potatoes in a large saucepan and cover with boiling water. Simmer gently for 10 minutes then drain and slice.
3. Dissolve the cornflour in a little cold water and stir into the lamb mixture. Simmer for 1-2 minutes, then transfer to a large ovenproof dish. Stir in the olives and ¾ of the feta. Thinly slice the remaining tomatoes and lay on top of the mixture followed by the sliced potatoes. Brush the top with a little oil and scatter over the reserved feta. Bake for 15-20 minutes until golden brown. Serve with greens.
Leftover mashed potato makes a great alternative topping to the sliced potatoes used in this pie.