Boil corn in a large pot of salted, already-boiling water and boil for 3-5 minutes, until tender. Remove from heat and shuck into a large bowl. Set aside.
In a medium bowl, toss avocados with lemon juice.
Add avocados, tomatoes, red peppers, onions, and lime zest into the bowl with the corn.
In a medium bowl, whisk lime juice, olive oil, salt, pepper, and garlic. Pour over the large bowl of other ingredients.
Gently toss all ingredients together and refrigerate until ready to serve.
Just before serving, toss in cilantro.