Heat the oil in a large pan. Add the minced beef and cook until browned. Add the vegetable hot pot and carrots. Simmer for 20 minutes.
Meanwhile bring a large pan of water to the boil and add the two types of potatoes. Simmer for 15 minutes or until tender. Drain, return to the pan and mash with the mustard, milk and butter.
When the mince is cooked, check the seasoning and spoon into an ovenproof dish. Spread the mashed potato over the meat and sprinkle with the cheese. Place under a preheated grill fro 5-10 minutes or until the top is beginning to turn brown.