Preheat the oven to 400 degrees F. Rub each bread slice with the cut side of the garlic and set on a baking sheet (safe leftover garlic for another use). Drizzle the bread with 1 Tbsp. of the olive oil. Bake the bread 8 to 10 minutes, or until lightly toasted. Remove bread from the oven and set aside.
Heat the other 1 Tbsp. olive oil in a large nonstick skillet set over medium heat. Add the mushrooms and rosemary and cook until mushrooms are tender and all the moisture has been cooked out of them. Removed from the heat and season with salt and pepper.
To serve, spread each toasted piece of bread with goat cheese and set on a platter. Divide and mound the bread with the mushrooms. Drizzle each bruschetta with a little balsamic vinegar. Garnish each bruschetta with a small rosemary sprig, if using, and serve.