Place all chermoula ingredients in a food processor and blend, add the olive oil until you make a marinade. Brush the tuna with half the marinade and leave to rest for 15 minutes. Heat the BBQ until very hot. BBQ the tuna for 2 minutes on every side leaving it with a pink colour in the middle. Let it rest for 3 minutes. Serve with the rest of the chermoula and other side salads.