Mix together all of the sauce ingredients in a medium bowl, cover, and let sit at room temperature for at least 1 hour and up to 2 hours before serving.
Heat your grill to high.
Toss the prawns with the oil in a bowl and season with the salt and pepper. Grill the prawns for 2 to 3 minutes per side, or until just cooked through. Remove to a platter and immediately spoon the sauce over shrimp with a slotted spoon. Serve hot.