Bring broth to a simmer. Adjust heat to maintain a steady simmer.
Heat oil in a large pan or dutch oven over medium-high heat.
Add onion and garlic and sweat, stirring, until the onion is translucent, about 2 minutes.
Increase the heat, add mushrooms and cook, stirring, until they begin to release their juices, 2 to 3 minutes.
Add barley and cook, stirring, for 1 minute.
Ladle chicken broth to barley a little at time and stir until all the stock has been absorbed into the barley grains. you may not necessarily use all your stock as it may get too mushy.
Stir in spinach and cook, stirring, until it is wilted, about 1 minute.
Stir in cheese, butter and parsley. Season with pepper and salt.
Serve and enjoy.