Cook the pasta according to the instructions on the packet, drain and allow to cool.
Wash the tomatoes, rocket and chives. Quarter the tomatoes and cut the chives into small rolls.
For the dressing, mix oil, vinegar, mustard, salt and pepper, I like to do it in a screw-top jar, which I then close and shake well.
Add tomatoes, chives, tuna and rocket to the pasta and mix everything together. Pour the dressing on top and fold in. Let the salad steep for about 4 hours.