Ingredients:4 large portobello mushroom caps2 teaspoons olive oil1 1/2 tablespoons balsamic vinegar1/4 teaspoon coarse salt1/2 teaspoon freshly ground black pepper, divided1 1/2 cups chopped tomato1/3 cup chopped kalamata olives1 cup fresh whole-grain breadcrumbs1/2 cup (4 ounces) shredded fontina cheese1/4 cup chopped fresh chives