Prepare the Corn: Remove the husks and silk from the corn, trim off the stems, then brush the surface of each cob with high-heat oil.
Heat the Pan: Place a cast iron skillet or grill pan over medium heat and let it heat for at least 5 minutes so the pan becomes very hot before adding the vegetables.
Char the Corn: Place the oiled corn cobs in the hot pan. Cook for about 15 minutes total, turning the cobs occasionally, until the kernels become bright in color and some develop deep char marks.
Prepare the Zucchini: While the corn cooks, slice each zucchini in half lengthwise. Brush all sides with oil.
Prepare the Onion: Cut the red onion into thick rings and brush the surfaces with oil.
Char the Zucchini: Once the corn is finished, transfer it to a cutting board to cool slightly. Place the oiled zucchini in the hot pan and cook each side until well charred, about 10 minutes total. Char the Onion: Remove the zucchini and place the onion rings in the pan. Cook them until charred on each side, about 5 minutes total.
Chop the Vegetables: Cut the zucchini into half-rounds or quarter-rounds. Chop the charred onion into small pieces and roughly chop enough cilantro to measure 1/4 cup. Combine the Vegetables: Add the chopped zucchini, onion, and cilantro to a large mixing bowl.
Remove the Corn Kernels: Stand each corn cob upright on a cutting board and carefully run a sharp knife down each side to cut away the kernels. Add the kernels to the bowl.
Season the Salad: Add a couple of generous pinches of salt and pepper to the vegetables, then toss everything together until evenly combined.
Add the Feta: Crumble the feta over the salad and gently toss once more to distribute it without heavily breaking it apart.
Serve the Salad: Serve the salad immediately while slightly warm, or refrigerate it for later and serve it cold.
