Begin to heat the broth to almost a boil, keeping hot until ready to use.
In a large pan, briefly saute onion and garlic in olive oil, about 2 minutes. Add the barley and cook, stirring often, until the barley begins to brown, about 5 minutes.
Add hot broth, sherry, and zucchini to the barley and bring to a boil. Reduce heat to a simmer, cover and cook for about 1 hour, stirring occasionally.
Remove the lid and stir in the Parmesan. Cook an additional 10 minutes without the lid.