Preheat your grill or grill pan over medium-high heat until hot and slightly smoky.
Place the corn on the grill, turning occasionally, until the kernels are charred in spots and the husks are blackened, about 10-12 minutes. The kernels should be tender and smoky.
Carefully peel back the charred husks, working quickly to avoid burning your fingers. The kernels underneath should be smoky and slightly glossy from the natural juices.
In a small bowl, mix the mayonnaise with chili powder for a spicy, tangy coating. Whisk until well combined and set aside.
Brush the hot, charred corn generously with the spicy mayonnaise using a basting brush, ensuring the mayo melts into the kernels and creates a sticky coating.
While the corn is still hot, sprinkle crumbled Cotija cheese over the top, allowing it to melt slightly into the mayo coating.
Squeeze fresh lime juice over the corn for brightness and sprinkle with chopped cilantro if using.
Serve the corn immediately on a platter, garnished with extra cheese or lime wedges if desired, and enjoy the smoky, gooey, spicy bites.
