Blend basil leaves, mayonnaise, and shallot in processor until smooth. Gradually blend in buttermilk and lemon juice. Season dressing to taste with salt and pepper. (Can be made 1 day ahead. Cover and refrigerate.) Mix Asiago cheese, currants, and pumpkin seeds in medium bowl. Using 1/6 of couscous, 1/6 of arugula, 1/6 of tomatoes, 1/6 of chicken, 1/6 of corn, and 1/6 of Asiago cheese mixture, form rows on each of 6 plates. Serve, passing dressing separately. * Available at specialty foods stores and some supermarkets.