In a large, heavy-bottomed pot, heat olive oil over medium-high heat. Sweat onions until soft and translucent. Add garlic and cook until fragrant, about 30 seconds. Add mushrooms, stirring frequently, cooking until vegetables are caramelized and fragrant. Stir in soy sauce. Cover with stock and bring to a simmer. Add barley, cover and cook 20 minutes. Remove soup from heat. Stir in kale and thyme leaves. Divide into bowls and serve.