Place the lamb, onion, carrot. stock, thyme or rosemary, garlic pumpkin, salt and a few twists of freshly ground black pepper in the slow-cooker. Set on low and cook 7-9 hours. (Alternatively, pre-heat the oven to 355℉ fan [390℉]. Put everything in a large casserole dish, cover with a tightly fitting lid and cook for 3 hours. Stir once or twice during cooking, adding a little water if it starts looking dry.)
When nearly ready to eat, prepare the Creamy Cauli Mash and set aside, covered to keep warm.
Add the broccoli florets to the slow-cooker (or casserole), cover and cook for another 4-5 minutes. Add the silverbeet, stir through the dish and season to taste wit salt and pepper.
Serve the lamb shanks in large bowls with a generous dollop of cauliflower mash alongside.