Heat the oil in a skillet
Saulte the onion and garlic until lightly browned
Mix in the harissa and the lemon and give it a quick stir
Transfer to a blender and add the coriander leaves and a little bit of red food colour, if you like
Blend to a paste
Stick the prawns lengthwise in skewers and coat with the marinade
Set the prawns aside for about 30 minutes
Then grill them on a conventional outdoor grill or at the highest setting in your oven, until done
