Preheat oven to 150C. Heat olive oil in a casserole over high heat, add lamb neck and turn occasionally until brown (3-4 minutes). Remove lamb from pan and set aside. Reduce heat to medium, add onion and garlic and sauté until tender (4-5 minutes). Add spices and stir until fragrant (1 minute), then return lamb to casserole with pumpkin and chicken stock. Add tomatoes and coarsely crush, then season with sea salt and bring to a simmer. Cover and bake until flesh falls from the bone (3 hours). Serve with couscous.