Sauté onions in oil until translucent. Add sliced mushrooms and sauté until shrunken, about 15 minutes.
Add garlic cloves, soy sauce, kosher salt, black pepper, and water. Bring to a boil and then simmer for about an hour.
In a separate pot, cook barley in 2 ½ cups of water for about 45 minutes, until tender. Strain any leftover liquid. Set aside. Using an immersion blender, blend soup until piecey - not smooth. There! Nobody will have to see the onions they’re eating!