Sheet Pan Cod and Potatoes

Name: Sheet Pan Cod and Potatoes
Ingredients: 1 pound small Yukon Gold potatoes, halved; ½ cup olive oil, divided; 1 ¼ teaspoons kosher salt, divided; ¾ teaspoon freshly ground black pepper, divided; 4 6-ounce cod fillets; 2 bunches Swiss chard, stems removed and leaves chopped; ½ cup pitted green olives (such as Castelvetrano), halved; 3 tablespoons fresh lemon juice (from 2 lemons); 1 tablespoon chopped fresh flat-leaf parsley leaves; 1 tablespoon finely chopped shallot; 1 ½ teaspoons Dijon mustard