How to Make It
Light a grill. In a mini food processor, combine the poblano, garlic, scallion, cilantro, lime juice, salt and sugar and puree. With the machine on, add 6 tablespoons of the oil in a thin stream.
Rub the corn with the remaining 1 tablespoon of oil and grill until lightly charred. Cut the kernels off the cobs.
Arrange the chicken on plates and surround it with the watercress, grilled corn, tomatoes and avocado; season lightly with salt and pepper. Pass the poblano vinaigrette at the table.