If using fresh ears of corn, prepare outdoor grill with hot coals, or heat gas grill to hot, or heat oven broiler. Brush husked ears with oil. Grill or broil ears about 6 inches from source of heat until golden-brown, about 8 minutes. Let corn cool to room temperature. Cut whole kernels from the cobs.
Stir together corn kernels, olive oil, salt and pepper in medium-size bowl until well mixed. Add diced avocado, diced tomato, minced jalapeño, chopped cilantro and lime juice; gently stir to mix well; avoid mashing pieces of avocado. Makes 3 cups.