In a medium-large pot or Dutch oven, pour in 2 tablespoons of vegetable oil and heat over medium-high until it shimmers, about 2 minutes.

Add 1 medium-sized chopped onion, 1 teaspoon of minced garlic, and 1 cup of thinly sliced carrots. Sauté for about 4 minutes until the onion is translucent and fragrant.

Incorporate 2 cups of thinly sliced brown mushrooms into the pot and sauté for an additional 3 minutes until they start to release moisture and slightly brown.

Stir in 1 cup of rinsed pearl barley, followed by enough water (approximately 5-6 cups) to cover the vegetables by 4 inches. Add in 1 tablespoon of vegetable stock powder and season with salt and pepper.

Increase the heat to high, bringing the soup to a boil while stirring occasionally. Once boiling, reduce the heat to low and cover the pot. Let it simmer gently for 1 hour.

If using a slow cooker, transfer the sautéed vegetables and all ingredients into a slow cooker and cook on low for 6-7 hours.

Test the barley for a tender but chewy texture, then ladle the soup into bowls. Garnish with freshly chopped parsley before serving.