Over a gas range, place the ear of corn on the grate, and cook, rotating the corn a quarter turn every minute or so. Do this until the outside is evenly charred and the corn is tender, about 5-7 minutes. Transfer the corn to a cutting board and when the corn is cool enough to handle and cut the corn kernels off the cob. In a medium bowl, mix together the corn, jalapeño, red onion, summer squash, juice from 2 limes, queso fresco and cilantro. Salt and pepper to taste. Set aside.
Slice the summer squash into batons. In a shallow plate, mix together the bread crumbs, ground mustard, ground cayenne and salt. In a small to medium bowl, beat together the two eggs.
One by one, dip the squash batons in the beaten eggs and transfer to the plate, tossing them with the bread crumb mixture, being sure to coat the squash thoroughly. Repeat the process until all of the squash batons are coated.