1. Gather the ingredients.
2. Mix the sauce ingredients together in a bowl. Set aside.
3. If grilling prawns without shells, skip the next two steps. To grill the prawns in their shells, you need to butterfly them so they lay flat in their shells on the grill. Uncurl the prawn, belly-side facing upwards. Cut a line from underneath the head of the prawn to the tip of the tail using a sharp knife, making sure the knife cuts through the meat but not the outer shell of the prawn.
4. Open up the prawn fully. Remove the black intestinal tract from the prawn by scraping it out with the tip of a sharp knife. Now turn the prawn over on your cutting board (so that its back is facing up). Use your palm to flatten it out by pressing down gently. When you're done, the prawns should lay fairly flat (don't worry if the shell loosens slightly).
5. Place the prawns in a flat-bottomed bowl or dish. Pour over the garlic sauce. Allow prawns to marinate in the sauce while you warm up the grill.
6. If your prawns are large enough that they won't fall through the grates, place directly on the grill. If your prawns are smaller, spread a piece of aluminium foil or banana leaf on the grill first, and then place prawns on top. Or skewer the prawns with satay sticks (if wood, soak in water first)
7. Baste the prawns the first time you turn them with a little of the leftover sauce. Grill 3 to 5 minutes each side. Prawns are done when the flesh turns from translucent to pinkish-white (and the shells turn a very attractive bright pink).
8. Serve immediately with fresh lime or lemon wedges on the side and a sprinkling of fresh coriander. They are equally excellent on their own or with rice.