Combine first 7 ingredients in a medium bowl. Toss in the prawns. Marinate at room temperature 30 minutes. Preheat an indoor or outdoor grill to medium-high. Set on the prawns, season with salt. Grill 1 to 2 minutes per side, or until just cooked through. Arrange on a platter and garnish with lemon slices. If desired, for added richness, drizzle prawns with a little melted butter before serving.
Note: After peeling, if you wish to devein the prawns, use a small paring knife to make a lengthwise slit along the back of each prawn. Pull out, or rinse out with cold water, any dark vein material. Pat prawns dry before using.