Preheat an outdoor grill for medium-high heat and lightly oil the grate.

Grill corn in the husks on the preheated grill, turning occasionally, to desired tenderness, about 15 minutes; some charring is fine. Remove from the grill. Remove and discard husks and silk when cool enough to handle. Cut kernels off into a medium bowl.

Add lime juice and chili powder, then mix in cotija cheese, cilantro, mayonnaise, and pepper until thoroughly combined. Taste and add salt if necessary.