Transfer the frozen corn to a colander and place it in the sink. Rinse the corn with cold water for a couple of minutes, tossing with your hands occasionally to break it up. Continue rinsing and tossing until the corn is thawed. Drain well. If using fresh corn remove the husks and silks and use a sharp knife to slice the corn from the cob.
Add the corn, tomatoes, mangoes, avocados, red onion, jalapeno (if using) and cilantro to a large mixing bowl. Set aside.
In a separate small bowl combine the rice vinegar, olive oil, lime juice, and a touch of sea salt. Pour the dressing over the salsa and toss lightly to avoid bruising the avocado.
Serve immediately or cover tightly with plastic wrap and refrigerate. It’s best if served within an hour or two.