Rinse the matjes fillets, pat dry and cut into bite-sized pieces. Peel the mango, cut the pulp from the stone and dice. Wash the cucumber thoroughly, cut in half lengthways, remove the soft inside with a teaspoon and dice the rest. Finely dice the peeled onion. Finely chop the chilli pods without the seeds and the white partitions.
Mix the lime and orange juice, salt, pepper and sugar into a marinade, fold in the oil. Add the dressing to the prepared ingredients and mix everything carefully.
Cover and let steep for half an hour and season to taste before serving.