Heat a large dry frying pan over a high heat. add the beef and onion and cook for 3-4 mins until the meat is browned. Stir in baked beans, worcestershire sauce , dried mixed herds and a dash of water. Season to taste.
Simmer rapidly for 3-4 minns, until thickened. Tip into a deep baking dish. Meanwhile preheat the grill on high. Spoon the mashed potatoes over the mince and smooth out the surface. Pop under the grill until golden and bubbling.