Start by de-veining the prawns. Use a small sharp knife to make a shallow incision down the back of each prawn, exposing the intestinal tract. Use the tip of the knife to lift out this vein – it won’t be visible in all cases, only if there are brown/black spots along the length of it. Set the prepared prawns aside.
Bring a saucepan of water to the boil, add the tagliatelle and cook for 10 minutes, or according to the packet instructions until tender.
Meanwhile, heat a medium lidded saucepan and spray lightly with the cooking spray. Add the tomatoes, chilli and seasoning then cook over a medium-high heat for 3-4 minutes until the tomatoes start to break up.
Add the prawns and 4 tablespoons of the pasta cooking water to the pan with the tomatoes. The prawns will start to turn from grey to pink as they soon come into contact with the heat. Cover the pan and cook gently for 3 minutes, stirring once or twice, until the prawns are cooked and pink throughout. Take care not to overcook the prawns or they will be dry, tough and rubbery.
Drain the tagliatelle and return to the pan. Add the prawns in the tomato sauce then add the rocket and lemon zest. Toss everything to mix together and serve in warmed bowls.