In a skillet over medium heat, saute the beef in the oil for 5 minutes, or until browned. Stir in the salt, pepper and garlic powder and place seasoned meat in a slow cooker. Add a little water to the skillet and stir to pick up the browned bits. Add to the slow cooker.
Add the broth, water, celery, carrots, green onions, parsley and barley. Cover and cook on low setting for 6 to 8 hours, or until the vegetables and barley are tender. Add the thyme just before serving.