Heat a medium-large pot over medium-high heat and add vegetable oil. Once shimmering, toss in the chopped onion, minced garlic, and thinly sliced carrots. Sauté for about 4 minutes until the onions turn translucent.

Add the thinly sliced brown mushrooms to the pot and sauté for an additional 3 minutes until they start to brown and release their umami flavor.

Stir in the barley, ensuring it’s well coated with the sautéed vegetables. Slowly pour in water or broth until the mixture is covered. Sprinkle in the vegetable stock powder, salt, and ground black pepper, and bring to a rapid boil.

Reduce the heat to low and cover the pot. Let the soup simmer for about 1 hour, stirring occasionally.

For a slow cooker option, transfer the sautéed vegetables to a slow cooker, add the barley, water or broth, and seasonings. Set it to cook on low for 6-7 hours.

Once finished cooking, ladle the soup into bowls and sprinkle with fresh parsley. Pair with crusty bread if desired.