Halibut with Tomatoes, Rosemary, and Zucchini in Foil Packets

medium zucchini, quartered and cut into 1-inch pieces

cherry tomatoes

pitted kalamata olives, halved

(6- to 8-ounce) skinless halibut fillets

salt

black pepper

garlic cloves, thinly sliced

sprigs fresh rosemary

olive oil

Hot cooked couscous