1. Heat oil in a large heavy-bottomed saucepan or soup pot over medium high heat. Add garlic and cook, stirring until fragrant but not browned, 30 seconds to 1 minute. Add celery, carrot, mushrooms, Italian seasoning, salt and pepper and cook, stirring often, until mushrooms have released their juices and vegetables start to soften, 4 to 6 minutes.
2. Add wine, increase heat to high and bring to a boil. Boil until wine is almost completely evaporated, about 4 minutes. Add broth, cover and bring to a boil. Reduce heat to low and simmer until vegetables are soft, 5 to 8 minutes. Stir in barley, chicken and scallions, increase heat to high and cook until heated through, 1 to 3 minutes.