1.Preheat oven to 220°C (200°C fan-forced). Line two large oven trays with baking paper.
2.Divide vegetables between trays. Cut three slashes crossways into the thickest part of each fish on both sides; place on vegetables. Top fish with lemon slices, drizzle with oil; season.
3.Bake fish and vegetables for about 25 minutes, or until fish is cooked through (the flesh in the slits will appear opaque).
4.Meanwhile, to make pumpkin seed pesto: In a mini processor, process seeds, basil, garlic, rind and juice for about 1 minute, or until well combined. With the motor still running, gradually add combined oil and water in a steady stream; process until smooth.
5.Divide fish and vegetables among plates; serve with pesto.
If you have both trays in the oven at the same time, to ensure even cooking, either swap the trays halfway through cooking time or use the oven’s fan-forced function. You can use four 250g pieces of salmon fillet instead of the barramundi, if you like. You will need to reduce the cooking time slightly.