Rinse lamb and pat dry. Arrange pieces close together on a flat surface and season one side with 1/4 teaspoon salt and 1/4 teaspoon of pepper. Heat 2 teaspoons olive oil in a large soup pot over medium heat. Add about half of the lamb, seasoned side down and sprinkle unseasoned side with 1/8 teaspoon salt and 1/4 teaspoon pepper. Brown all sides, forming a nice brown crust on the meat. Use a long fork or slotted spoon to transfer browned meat to a plate lined with paper towels. Pour most of the liquid out of the pot. Add two teaspoons olive oil, and repeat browning, seasoning, and draining process with the remaining meat.

Add remaining 2 teaspoons of oil to the pot. Add onions, 1 cup diced carrots, and 1 chopped mushroom. Sprinkle with flour and cook to soften onions, about 5 minutes. Add garlic and cook 30 seconds. Return lamb to the pot.

Pour in beef broth and scrape up brown bits on the bottom of the pot. Stir in tomato paste. Add Worcestershire, thyme, bay leaves, and half of the potatoes. Raise heat to high, bring to a boil, cover and simmer about 1 hour. Do not open the lid.

Stir in remaining potatoes, halved carrots, mushrooms, parsnip and barley. Cook on low for 30 minutes. Add the peas and cook 15 to 30 more minutes. Taste and adjust pepper and salt, if desired. Remove bay leaves. Garnish with fresh parsley before serving.