Heat oven to 200C/180C fan/gas 4. Heat the oil in a large pan and add the minced beef. Cook for 5 mins until browned all over, then add the carrot and cook for 2 mins more.
Stir in the tomato pure?e and add seasoning. Cook for a few mins, then add the lentils and stock. Simmer for 20 mins, then stir in the peas.
Meanwhile, bring a pan of water to the boil and add the potatoes. Simmer for 15 mins, then add the cauliflower and simmer for a further 10 mins until the veg is tender.
Drain, then return the veg to the pan for a few mins to dry out. add the milk, butter and seasoning, and mash together. Finally, add the cheese, reserving a handful, and mix well. Cover and put aside 500g of the mash mix for the sausage recipe tomorrow (see 'goes well with', right).
Spoon the mince into a large roasting dish, about 30 x 20cm, and spoon the mash over the top. Sprinkle with cheese and bake until golden, about 30 mins.