Heat the oil in the frying pan and add the onion, garlic, carrots and picked thyme leaves. Cook over a medium heat for 6-7 minutes, stirring occasionally, until beginning to soften. Add the mince to the pan, increase the heat and fry for 10 minutes, stirring all the time, until no longer pink. Stir in the baharat spice and tomato puree and cook, stirring for a further 1 minute.
Stir in the stock and bring to the boil. Season to taste. Reduce the heat to medium and simmer for 20 minutes, stirring occasionally. Stir in the courgette after 10 minutes.
Meanwhile, boil the butternut squash and sweet potato according to pack instructions. Drain well, then mash until smooth. Season to taste.
Preheat the oven to 200°C/gas mark 6. Spoon the lamb mixture into a 2-litre ovenproof dish. Spoon the mash over the top to cover completely. Season with freshly ground black pepper and garnish with the extra thyme leaves. Bake for 30-35 minutes, until golden and bubbling.