Heat oil in a skillet over medium heat. Add beef and sauté until browned, about 5 minutes. Stir in garlic powder, salt, and pepper, then transfer mixture to a slow cooker.
Add a few tablespoons water to the skillet. Stir over medium heat, scraping up any browned bits with a spoon. Transfer liquid and browned bits to the slow cooker.
Add remaining water, broth, carrots, green onions, celery, barley, and parsley. Cover and cook on Low until vegetables and barley are tender, 6 to 8 hours.
Stir in thyme just before serving.
Notes
This recipe is perfect for a comforting meal during cold weather.