Heat olive oil in a large pot over medium-high heat. Season beef with salt and pepper. Brown half the meat in a single layer for 3-5 minutes per side; repeat with remaining meat.
Remove meat and keep warm. Add onion, carrots, celery and garlic; cook 4-5 minutes until softened. Vegetables may be left in for softer texture or reserved and returned later.
Add beef, broth, bay leaf and thyme. Bring to a simmer and cook 60 minutes or until beef is tender.
If vegetables were reserved, return them now. Add barley and mushrooms; cook 20-30 minutes until barley is tender.
Season with salt and pepper, sprinkle with parsley and serve.