Grilled Ratatouille Muffaletta

Name: Grilled Ratatouille Muffaletta
Ingredients: 1 medium eggplant , sliced into ½-inch-thick planks; 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-thick rounds; 1 medium zucchini , sliced into ¼-inch-thick planks; 1 jar (12 ounces) roasted red peppers , patted dry; 1 (8-inch) round loaf rustic bread , split horizontally and hollowed out