Squeeze the lemon and orange and measure 50 ml each. Cut the chilli pepper into fine rings and finely chop the coriander. Halve the vanilla pod lengthways and scrape out the pulp. Put all ingredients in a freezer bag and mix together. Also add the scraped out vanilla pod to the marinade. Add the prawns and marinate in them for at least 3 hours. To do this, move the freezer bag at intervals and mix the prawns with the marinade and let them steep.