Grilled Cubano Sandwich

Name: Grilled Cubano Sandwich
Ingredients: One 1-pound pork tenderloin; 1/4 cup plus 1 tablespoon yellow mustard; 2 tablespoons extra-virgin olive oil, plus more for oiling the grill grates; 8 dill pickle slices (cut lengthwise), plus 2 tablespoons pickle brine; 2 small cloves garlic, grated; Kosher salt and freshly ground black pepper; One 14-inch loaf Cuban bread or other long, soft bread, split lengthwise; 2 tablespoons salted butter, melted; 1/4 cup mayonnaise; 8 ounces thinly sliced deli ham; 4 ounces thinly sliced Swiss cheese