Cook the pasta in boiling water for 10-11 mins. Just before the end, add prawns and cook through. Drain, cool under cold water, drain and transfer to a big bowl.
Put the oil, lemon juice and zest, garlic, avocado, tomatoes and spring onions in a separate bowl, then mix well – don’t mash the avocado. Season. Gently toss the mix into the pasta, with the rocket and basil.