Heat 1 tbsp of the oil in a saucepan. Add one of the chopped onions and fry for 2 minutes. Then add the carrot, red pepper and mushrooms, and fry for 3 minutes. Add the garlic, then the chopped tomatoes.
Bring up to the boil and simmer for about 15 minutes until the vegetables are soft. Blend until smooth with a hand blender.
Heat remaining oil in a saucepan. Fry the second onion for 2 minutes. Add the beef and brown then coat in the flour. Add the stock, cooked vegetables, thyme, Worcestershire sauce and sugar. Season and simmer for 30
Cook the potatoes in boiling lightly salted water until soft, drain, then mash with the milk and butter. Spread the potato over the mince and sprinkle with the cheese.
Preheat the oven to 220°C/gas mark 7. Bake for 20 to 25 minutes until bubbling and tinged brown on top.