Bring a large pot of salted water to a boil. Boil the corn for 3 to 4 minutes until tender-crisp, being careful not to overcook. Drain the corn and immediately immerse it in very cold water to stop the cooking. Place the corn on a clean dish towel set over a cutting board, then use a serrated knife to cut the kernels off the cobs.
Combine all ingredients except for avocados in a large bowl and mix well. Cover and chill for a few hours or overnight.
Right before serving, add avocados and mix gently, being careful not to mash avocados. Garnish with more chopped cilantro if desired. Serve at room temperature.
