Heat your grill to high, approximately 400°F.
Husk corn, then roast it on the grill for about 20 minutes, turning every 5 minutes. Watch the corn closely so it doesn't burn. Remove the corn from the grill and allow it to cool completely. Carefully cut the corn kernels from the cob.
Add the roasted corn, mayonnaise, cotija cheese, lime juice, chili powder, cilantro, green onions, jalapeños, Tajín, salt, and pepper to a large bowl.
Stir until all the ingredients are well combined.
Refrigerate in an airtight container until chilled.
Before serving, garnish with additional cotija cheese and chopped cilantro.
Serve chilled with tortilla chips or your favorite dippers.