Heat the oven to 375°F. While the oven is heating, add oil to a large skillet over medium to high heat. Add the ground lamb, onion, and garlic to the skillet and cook until the lamb is brown, stirring often to separate meat. Drain off any fat and transfer to a large bowl.

Stir in carrots, green beans, mushrooms, ketchup, tomato paste, Worcestershire sauce, rosemary, and garlic powder. Stir until combined and season with salt/pepper to taste.

Pour the lamb mixture into a 13x9 inch casserole dish and spoon the mashed potatoes on top. Drizzle the melted margarine and Parmesan cheese on top and bake for about 40 minutes or until the topping is lightly browned.

Enjoy!