Tip the onions, carrots, celery and olive oil into a large saucepan. Cook over a medium heat for 8-10 mins until softened, add the garlic and fry for another minute. Pour in the wine to deglaze the pan (scraping up any bits stuck on the bottom), and simmer for 2 mins until most of the wine has evaporated.

Add the thyme, tomato purée, soy sauce, caster sugar and vinegar to the pan and stir to combine. Tip in the lentils, tomatoes and 100ml water and simmer for 10-12 mins until reduced and thick enough to coat the back of a spoon.

Meanwhile, make the mash topping. Bring a large pan of water to the boil, add the sweet potatoes and simmer for 10-15 mins until cooked all the way through. Drain, then add the dairy-free margarine, mustard powder and milk, and mash until smooth along with plenty of salt and pepper.

Heat the oven to 200C/180C fan/gas 6. Season the filling and pour it into a 25cm x 20cm x 7cm casserole dish. Top with the mash, starting with spoonfuls on the outside corners and working your way inwards so the filling doesn’t spill out. Sprinkle the pumpkin seeds on top and bake for 30-35 mins until golden and bubbling. Once baked and left to cool, the pie will keep frozen for up to three months. Defrost thoroughly overnight, then reheat in the oven until piping hot.