In a small, tightly covered saucepan, cook barley with broth on low until barley is split but not soft. If water is not fully absorbed, strain and set aside.
In a large skillet, heat olive oil over medium heat. Sauté onions until caramelized. Add garlic and cook until fragrant, about 30 seconds. Add mushrooms and cook until mushrooms let down their water, 20-30 minutes. Add cooked barley and combine. Taste for seasoning and garnish with dill before serving.