Prep your onion, carrots, and celery. Add them to a large pot along with the olive oil over medium-high heat. Sauté for 5-7 minutes, stirring occasionally.
Meanwhile, chop the mushrooms.
Stir the mushrooms into the pot and sauté for another 5 minutes.
Add the Italian seasoning, garlic, vegetable broth, water, and barley to the pot. Increase heat to high and bring the soup to a gentle boil. Reduce heat to medium and simmer for 25-30 minutes or until the barley is cooked (it should be al dente, not mushy).
Season with salt & pepper as needed. Garnish with parsley if desired.
