BBQ Eggplant Sandwiches with Provolone and Mushrooms recipes

Name: BBQ Eggplant Sandwiches with Provolone and Mushrooms recipes
Ingredients: 1 large eggplant (about 1 1/2 pounds), trimmed and sliced lengthwise into four 1/2-inch thick planks; 1/2 cup BBQ sauce, divided; 1 teaspoon kosher salt; 1/2 teaspoon freshly ground black pepper; 8 ounces cremini mushrooms, thinly sliced; 1 red onion, halved and sliced into thin wedges; 2 tablespoons vegetable oil; 4 slices provolone cheese (1/8-inch thick slices); 4 ciabatta or hoagie rolls, split and toasted; 1/4 cup mayonnaise; 2 jarred pepperoncini peppers, thinly sliced