1Combine pearl barley and boiling water in a bowl; set aside to soak for 10 minutes.
2Heat canola oil in a large saucepan over medium heat. Cook and stir onion, celery, and carrot in hot oil until softened, 5 to 7 minutes.
3Stir mushrooms into the onion mixture; cook and stir until softened and brown, about 5 minutes.
4Drain the barley, discarding any remaining water from soaking. Stir the barley into the mushroom mixture.
5Stir the garlic and tomato paste into the mixture, stir until combined, then pour the beef stock into the sauce pan. Season with the oregano, salt, black pepper, and Worcestershire sauce.
6Bring the soup to a boil, reduce heat to low, and cook at a simmer for 1 hour.