Preheat your grill to medium-high. Place the first 7 ingredients in a food processor or blender and pulse until smooth; season with salt and pepper. Transfer to a small pot and bring to a slow simmer over medium-low heat. Place the prawns in a bowl and toss with oil, salt and pepper.
Grill the prawns 1 to 2 minutes per side, or until just cooked through. Pour a pool of the sauce on each of the 4 plates. Set 6 prawns on each pool of sauce and serve.