Preheat the oven to 220°C (200°C Fan) or Gas Mark 7.
Heat 1 tbsp of oil in a saucepan on a medium high heat. Fry half of the chopped onions until softened.
Add the carrot, pepper and mushrooms and fry until softened.
Add the chopped tomatoes and garlic. Evenly mix.
Bring to the boil and simmer for 15 minutes until the veggies are soft. Blend to desired texture with a hand blender (be careful because it will be hot).
Heat remaining oil in a saucepan on a medium high heat. Fry the remaining onion and then add the beef to brown.
Once fully browned, add the flour and ensure it is fully coated.
Add the stock, veggies, thyme, Worcestershire sauce. Season with salt and pepper and mix well. Leave to simmer for 30 minutes.
Boil the potatoes until soft. Drain and mash with milk, butter and salt and pepper to taste.
Pour mince into an oven proof dish then top with the mashed potatoes. Sprinkle cheese over the top.
Bake for 20-25 minutes until the top is a golden brown.