Heat the oil in a pan and fry the onion for 5-10 minutes until soft, adding the garlic for the last minute. Turn the heat up to medium/high, add the mince and cook for 5 minutes.
Stir through the tomato purée and mixed herbs, then pour in the stock. Bring to the boil, then simmer for 15 minutes, until thickened.
Preheat the oven to 200ºC/fan 180ºC/gas mark 6. Cook the sweet potatoes, potatoes and carrots in a pan of boiling water for 10 minutes until soft. Drain and mash with the dairy spread.
Spoon the mince mixture into a 1-2 litre-baking dish and top with the mash. Bake in the oven for 20 minutes. Meanwhile, cook the peas in boiling water for 2 minutes. Drain and serve as a side.