Chill salad up to 24 hours ahead before adding the avocado.
Preheat oven to 450°. Toss corn with 1 Tbsp. olive oil, and spread in a single layer in a jelly-roll pan. Bake 7 to 8 minutes or until golden brown. Cool 10 minutes. Combine corn, tomatoes, and next 2 ingredients.
Whisk together vinegar and next 5 ingredients in a large bowl; add tomato mixture, and toss to coat. Gently stir in avocado. Let stand 20 minutes, stirring occasionally. Top with basil just before serving.