In a heavy-bottomed pot, heat oil. Add onions, cooking until softened. Add lamb; cook until browned, then dust with flour. Mix thoroughly; cook an additional 1 minute. Add carrots, peas and corn; incorporate well. Add tomato paste and Worcestershire. Gradually add stock; bring to a boil then reduce to a simmer. Simmer on low approximately 10 minutes. Adjust seasoning with salt and pepper. Remove from heat. Stir in parsley; set aside to cool.
In a pot, cover the potatoes with cold water. Bring to a boil; reduce heat and simmer until potatoes are fork tender. Drain and steam dry. In a bowl, add heavy cream and butter. Grate potatoes, skin on; gently mix with cream and butter until semi-smooth with small chunks.
Spoon the cooked lamb mixture into a large casserole pan or 12 individual casserole dishes. Spread a layer of the smashed potatoes over the lamb mixture; top with shredded cheese. Bake at 375°F until internal temperature of 165°F is reached.