Heat the oil in a large shallow pan. Add the frozen onion and cook for 3 minutes to soften. Add the frozen meatfree mince and stir-fry for 3 minutes.
Add the stock and tomato purée, bring to the boil, then reduce the heat, cover and simmer for 5 minutes. Add the frozen sweetcorn and peas and cook for a further 3 minutes.
While the mince is cooking, defrost and heat the mashed potato in the microwave: put it in a microwave-proof bowl with 2 tbsp water, cover with cling film and cook on high for 5 minutes, stirring once. Cook the carrots in a pan of boiling water for 5-7 minutes, or until just tender.
Mix the cornflour with 1 tbsp cold water to make a paste. Stir into the mince mixture and simmer for a further 1-2 minutes until thickened and bubbling. Divide the mince between 4 x 500ml individual heatproof dishes. Preheat thegrill to high.
Stir the parsley into the mashed potato, then cover and microwave on high for 1 minute. Spoon the hot mash over the mince to cover, roughing up the surface with a fork. Place the dishes on a baking sheet and pop under the grill for 5 minutes until the potato is just golden. Drain the carrots and serve with the cottage pies.