1.Cut leek in half lengthways. Cut into 10cm lengths; separate layers. Drop leek into medium saucepan of boiling water; drain. Rinse under cold water; drain.
2.Shell and devein prawns.
3.Flatten garfish with rolling pin. Place fish skin-side down on board; line with pieces of leek, then a slice of prosciutto. Spread each with 1 teaspoon of the pesto; top with a prawn. Starting from head of fish, roll to enclose prawn; secure with toothpick. [Can be made a day ahead to this stage and refrigerated, covered.]
4.Cut zucchini lengthways into 5mm-thick slices. Cook on heated oiled grill plate (or grill or barbecue) until browned and tender. Cover; keep warm.
5.Cook fish on grill plate until cooked through. Serve fish with char-grilled zucchini.
Roasted vegetable pesto is available from most supermarkets; alternatively, you can use your favourite flavoured pesto.Note