To make the dressing:
Combine the sour cream, Tabasco sauce, and lime juice in a small bowl and set aside.
To make the relish:
Toss together the corn, onion, jalapeño, tomatoes, vinegar, 3/4 cup plus 2 tablespoons of the olive oil and the cilantro in a bowl and season to taste with salt and pepper.
To cook the prawns:
Remove the shell from the body of each prawn, leaving the head intact. Skewer the length of the prawn on a bamboo skewer. Season lightly with salt and pepper and brush with the remaining 2 tablespoons olive oil. Place on a hot grill for 30 seconds, brush with barbecue sauce, and grill for 30 seconds. Turn the prawns over, brush with more barbecue sauce, and grill for 1 minute. Remove the prawns from the grill and remove the skewers.
To prepare the greens:
Toss the mesclun greens with some of the liquid from the corn relish.
Place a mound of mesclun greens in the center of each plate and arrange the prawns on the lettuce. Spoon the corn relish in a band across the prawns and drizzle the dressing back and forth across the salad in a Z pattern.