Preheat grill to high (450 degrees F to 500 degrees F). Lightly coat corn and poblano with cooking spray. Grill, uncovered, until lightly charred and tender, 10 to 12 minutes, turning occasionally. Remove the corn from the grill. Continue to grill the poblano until it's totally charred and blackened on the outside, 3 to 5 minutes more. Let cool for 10 minutes.