Preparation / Directions:
Brush the corn with some of the additional oil and grill it on a rack set about 6 inches over glowing coals, turning it, for 15 minutes, or until it is golden brown.
Let the corn cool until it can be handled. Working over a bowl, with serrated knife cut the kernels from the cobs and with the back of the knife scrape the pulp from the cobs.
Brush the shrimp with some of the additional oil, grill them on the rack, turning them, for 6 to 8 minutes, or until they are cooked through, and transfer them to the bowl. Stir in the onion, the jalapeno, and the coriander.
In a small bowl whisk together the lemon juice, the vinegar, and salt and pepper to taste, add the remaining 1/3 cup oil in a stream, whisking, and whisk the dressing until it is emulsified. Pour the dressing over the corn mixture and combine the salad well. Divide the watercress among 6 plates and spoon the salad over it.