Heat the oil in a medium-large pot over medium-high heat until it shimmers.

Sauté the chopped onion and minced garlic until the onion becomes translucent, about 4 minutes. Add sliced carrots.

Incorporate sliced brown mushrooms into the pot and stir for about 3 minutes until browned.

Stir in barley and cover with water, bringing the mixture to a boil.

Season the soup with vegetable stock powder, salt, and pepper; reduce heat to low and simmer for 1 hour.

For slow cooking, transfer mixture to slow cooker and cook on low for 6-7 hours.

Serve the soup and garnish with fresh parsley.