Boil spaghetti in plenty of salted boiling water.
Meanwhile saute onion, garlic and chili in large frypan with olive oil until onion is soft. Add passata and semi dried tomtatoes and passata, season with salt and pepper.
Add prawns and half of the rocket and cook until prawns are just done.
Drain spaghetti and add spaghetti to the large frypan coating in the sauce. Serve on plate and place prawns on spaghetti and top with remaining rocket divided into 2.