Slice the (cooled and peeled) hard boiled eggs in half.
Use a spoon to carefully scoop out the yolk from the egg whites. Place the yolks in a bowl.
Add the mayonnaise, mustard, lime juice, chilli powder, and salt to the egg yolks. Add 2 tablespoon of the chopped onion, 2 tablespoon of the chopped cilantro, and half of the feta cheese, to the egg yolk mixture.
Mash all of the ingredients together with a fork. Use a stick blender or food processor to get a smoother texture. The smoother the mixture, the better it will pipe
Place the egg yolk mixture in a piping bar, equipped with a large star piping tip. Fill the egg white cavities with the filling, dividing it evenly. If you do not have a piping bag, you can use a spoon to fill the egg white cavities.
Use a knife to remove the roasted corn kernels from the cob. See notes for other roasted corn options.
Sprinkle the top of deviled eggs with the roasted corn kernels, and the remaining red onion, cilantro, and feta cheese.
Place the prepared Mexican Street Corn Deviled Eggs in the refrigerator until ready to serve.