Heat the oil in a large frying pan, add the onion, carrots, crushed chillies and garam masala, and cook for 5-10 minutes.
Meanwhile, put the sweet potato in a microwave-safe dish and cover with clingfilm. Microwave on high for 10 minutes, until very soft. Remove the clingfilm and then mash until smooth.
Add the mince and cook for a further 5 minutes until it has browned. Stir in the stock, peas and pasta sauce, bring to the boil then let simmer for 10 minutes. Pour the mixture into a 1-litre pie dish.
Preheat the grill to medium-high. Spoon the sweet potato mash over the mince mixture, and grill for 5-10 minutes, until golden.
Cook's tip: for vegetarians, simply replace the beef mince with vegetarian mince and the beef stock cube with a vegetarian one.