Preheat the oven to 180 degrees C. Heat the oil in a large flameproof casserole dish, add the chopped onion and garlic and cook, stirring, for 5 minutes or until softened. Add the cubes of lamb and cook for 5 minutes or until browned on all sides, stirring so they colour evenly.
Add the wine, stock, bay leaf, thyme, potatoes, carrots and pickling onions. Season with salt and pepper to taste. Bring to the boil, then cover with a tight-fitting lid and transfer the dish to the oven. Cook for 1 hour.
Add the turnips and stir together. Cover the casserole dish again and continue cooking for 30–45 minutes or until the meat and vegetables are tender, adding the peas 10 minutes before the end of the cooking time.
Add the parsley and stir well. Taste and add more salt and pepper if needed.