Mediterranean Cod Packets

Name: Mediterranean Cod Packets
Ingredients: 1 pound small Yukon gold potatoes, sliced about inch thick; 1 small onion, sliced; 1 clove garlic, minced; 3 tablespoons extra-virgin olive oil; 1/4 teaspoon red pepper flakes; Kosher salt; 4 skinless center-cut wild cod fillets (about 6 ounces each); 1/4 teaspoon finely grated lemon zest, plus 2 tablespoons lemon juice; Freshly ground pepper; 1 teaspoon chopped fresh thyme; 1/4 cup pitted kalamata olives, coarsely chopped; 1 15-ounce can cherry tomatoes; 2 tablespoons unsalted butter, at room temperature; 1 tablespoon chopped fresh chives