2) Prepare the griddle on a high heat. Using a knife, cut the back of the prawns. Brush the prawns with oil and sprinkle with salt. Griddle until just cooked through, about 3 minutes on each side. Transfer the prawns to a plate.
3) Meanwhile, cook the pasta in a large pan of boiling salted water until tender but still firm to the bite, stirring occasionally, about 8 minutes. Drain, reserving 120ml of the cooking liquid.
4) Toss the pasta with the pesto in the large bowl to coat, adding the reserved cooking liquid 1 tbsp at a time to moisten. Top with the griddled prawns. Garnish with the lemon zest and parsley and serve.