Preparation:
Lay out 4 pieces of foil wrap, each about 15-inches (38 cm) in length. In centre of each, place 1/3 cup (75 mL) zucchini and tomatoes, 1/4 cup (50 ML) red pepper, 1 tbsp (15 mL) olives, if using, and 1 tbsp (15 mL) onion.
Cut partially thawed fillets in half through thickest part. Place fish over vegetables, thin end of one piece overlapping thicker portion of the other. Spoon about 2 tbsp (30 mL) of dressing over fish and vegetables.
Close foil starting with longer ends, making a double fold in centre. Roll in sides and press to seal parcels. Place on baking sheet; bake in 375°F (180°C) oven for 20 to 25 minutes, until fish is opaque and flakes with a fork and vegetables are tender. (May also be cooked on barbecue with the lid down.)