Rosemary Flatbread with Goat Cheese

olive oil, divided

medium yellow onion, peeled and thinly sliced

campari tomatoes (cocktail tomatoes), whole or halved

kosher salt and freshly ground black pepper

goat cheese, at room temperature

fresh rosemary, minced and divided

chives, minced

Italian flat leaf parsley, minced

garlic salt

jarred roasted red bell pepper, about ½ cup

Balsamic glaze