Preheat the oven to 350 degrees.
Peel and chop the potatoes. Put in a pot of cold, salted water and bring to a boil. Cook until tender. Drain. Add the butter, milk and salt and pepper. Mash well. Set aside.
While the potatoes are cooking, heat the oil in a cast iron skillet. Add the ground lamb and cook until browned. Add the onion and garlic and saute for 5 minutes. Add the worcestershire sauce, onion soup packet and beef broth. Stir to combine. Stir in the frozen veggies and cook for 5 minutes. Set aside.
When ready, top the meat and veggie mixture with the mashed potatoes. Smooth out and top with fresh parsley.
Bake for 40 minutes or until golden brown.