Portobello Mushrooms with White Beans and Prosciutto

Name: Portobello Mushrooms with White Beans and Prosciutto
Ingredients: 4 large portobello mushroom caps, gills removed; 4 teaspoons olive oil, divided; 2 teaspoons balsamic vinegar; 1/4 cup finely chopped shallots; 2 teaspoons finely chopped garlic; 1 teaspoon chopped fresh rosemary; 1 can (19 ounces) cannellini beans, rinsed and drained; 1/4 cup reduced-sodium chicken broth; 1 ounce prosciutto, chopped; 2 tablespoons finely chopped flat-leaf parsley; 3/4 cup baby spinach; 2 tablespoons panko breadcrumbs; 2 tablespoons grated fresh Parmesan; Olive oil cooking spray