Heat the oil in a large soup pot set over medium-high heat. Season the lamb with salt and pepper. Working in batches if needed, cook the lamb until browned, about 3 minutes. Transfer to a plate. Add the onions to the pot and cook until soft and golden brown, about 5 minutes. Add the garlic and cook 2 minutes. Transfer to the plate with the lamb.

Remove the pot from the heat and whisk in the flour. Return the pot to the stove and add the wine. Stir until smooth, scraping up any browned bits that have cooked onto the bottom of the pot. Whisk in the stock and water. Add the lamb and onions and bring to a simmer. Cover and cook 1 hour.

Add the turnips, potatoes, and carrots. Simmer for 30 minutes, or until the vegetables are tender.

Meanwhile, bring a small pot of water to a boil. Add the barley and cook 30 minutes, or until soft. Drain and add to the soup.

Just before serving, stir in the lemon juice and parsley. Season with salt and pepper.