Place 2 sheets of baking paper (about 30 cm x 40 cm) on kitchen bench.
Divide zucchini over the centre of paper sheets. Place fish on zucchini. Spread fish with pesto. Top with tomatoes, olives and garlic.
Lift sides of paper and fold over fish, then fold in ends of paper to form parcels. Place parcels, seam-side up, on a large baking tray. Bake in a preheated 220 °C oven (fan-forced) for 20 minutes.
Meanwhile, boil, steam or microwave potatoes until tender. Drain. Transfer to a bowl. Drizzle with oil and season with freshly ground pepper.
Carefully open parcels. Serve fish with potatoes and rocket.