Caponata Panini

Name: Caponata Panini
Ingredients: 4 sourdough demi-baguettes or rolls, halved lengthwise; 4 slices provolone cheese, halved; 1 1/3 cups caponata, recipe follows; 1/4 cup olive oil; 1 medium onion, chopped; 1 celery stalk, chopped; 1 medium eggplant, cut into 1/2-inch cubes; 1 red bell pepper, cored seeded, and cut into 1/2-inch pieces; 1 (14 1/2-ounce) can diced tomatoes with juices; 3 tablespoons raisins; 1/2 teaspoon dried oregano; 1/4 cup red wine vinegar; 4 teaspoons sugar; 1 tablespoon drained capers; 1/2 teaspoon salt, plus more for seasoning; 1/2 teaspoon freshly ground black pepper, plus more for seasoning