Preheat the oven to 200°C, fan 180°C, gas 6. Put the potatoes into the oven and bake for 50 minutes or until cooked through.
Meanwhile, heat the oil in a wok or deep frying pan and fry the mince over a high heat, stirring to brown all over. Add the courgettes and mushrooms and cook for 2 minutes before stirring in the cinnamon. After 1 minute, add the juice, raisins or sultanas, tomatoes and stock, plus a good grinding of black pepper. Stir, then reduce the heat and simmer for 20 minutes.
Once the potatoes have cooled slightly, scoop their flesh into a bowl and, with a fork, mash together with the extra olive oil. Spoon the mince into an ovenproof baking dish and top with the mash. Bake in the oven for a further 10 minutes, or until the top of the pie is crisp and golden.