- Place water, barley, mushroom, marjoram and pepper in slow cooker. Cover; cook on low 6 to 7 hours.
- Brown beef in large nonstick skillet 6 to 8 minutes over medium-high heart, stirring to break up meat. Drain and discard fat.
- Add celery and green onion; cook and stir 3 minutes.
- Stir beef mixture and half-and half into slow cooker mixture. Cover; cook High 10 to 15 minutes or until beef is hot and vegetable are tender.
- Garnish with parsley if desired.