In a large bowl, whisk together the olive oil, lime juice, cilantro, salt, and pepper.
Add the corn, avocado, tomatoes, and onion and toss to mix. Serve at room temperature. Serves 4 to 6. Tips: Choose ears of corn with bright green husks that are tightly closed. The ends of the corn silk should be golden brown, not pale -- an indication that the corn was picked too early.