Fry the carrot and onion in olive oil over a medium heat until the vegetables are softened. Add thyme and minced lamb. Fry until meat is cooked and browned.
Add chicken stock along with tomato puree, ketchup and Worchester sauce. Simmer for 25 minutes until the liquid has reduced. Add peas to the mix and transfer to an oven-proof dish.
Preheat the oven to 180°C/350°F/gas mark 4.
While the oven is heating peel and cut the sweet potato into small chunk and cook until soft. Once cooked through drain the water. Mash until smooth. Season with salt and pepper and spoon the sweet potato on top of the meat mixture and pop into the oven for approx 20 minutes until the potato is crisp on top.