Char the poblano over an open gas flame or under a broiler, turning until skin is blistered and blackened on all sides, about 8 to 10 minutes. Transfer to a bowl, cover, and steam 5 minutes. Peel off skin, remove stem and seeds, and finely dice.
If using fresh corn, grill, boil, or saute until just cooked through. If using frozen, thaw completely and pat dry.
In a medium bowl, combine corn, diced poblano, jalapeno, red onion, cilantro, lime juice, salt, and pepper. Toss to combine.
Cover and refrigerate at least 30 minutes before serving.
Taste and adjust salt and lime before serving.