Cook the croissant noodles in salted water according to the instructions on the packet. Drain the tuna in a colander and then cut it up with a fork.
Drain the mandarins too. Peel the banana and cut into thin slices. Cut the olives into slices as well. Mix the pasta with the fruit as well as the olives and the tuna.
For the sauce, mix the oil, yoghurt and ketchup, season with salt, pepper and sugar and let it steep for at least two hours.