Soak the corn in its husks in a bowl of heavily salted water overnight in the refrigerator. Keep the ears submerged below the surface of the water with a plate weighted down with a heavy can.
Prepare and preheat your lump charcoal grill to medium low.
Put the corn, still in its husks, on the grill, cover, and cook, turning occasionally, for 20 minutes.
Meanwhile, in a large bowl, combine the garlic, jalapeño and a large pinch of salt. Add the lime zest, lime juice and olive oil and whisk to combine. Add the avocado, tomatoes, scallions and cilantro and toss gently to combine.
Remove the corn from the grill. When cool enough to handle, peel back the husks, discard the silk and slice the kernels off the cobs with a knife. Add to the bowl of vegetables. Toss to combine. Season with salt and pepper.