Grilled Ratatouille Muffaletta

Name: Grilled Ratatouille Muffaletta
Ingredients: 1 medium eggplant, sliced into ½-inch rounds; Coarse salt; ½ cup pitted mixed olives, such as Kalamata and Cerignola; 2 pepperoncini, stemmed; ½ cup fresh parsley; ¼ cup mayonnaise; ¼ cup olive oil, plus more for grilling; 4 small tomatoes (1 pound), sliced into ½-inch rounds; 1 medium zucchini, cut lengthwise ¼-inch-thick; 1 jar (12 ounces) roasted red peppers, patted dry; 1 (8-inch) round loaf rustic bread, split horizontally and hollowed out