Preheat a grill to medium-high heat (about 375°F-400°F). Using a brush, coat each ear of corn with oil to make sure it doesn't stick to the grill during cooking.
Place the corn onto the grill grates, cover and let cook for about 2-3 minutes, until the corn is cooked through and charred in some spots. Turn the cobs and repeat the grilling process until all the sides are cooked and browned. Remove the corn from the grill and transfer to a large plate or baking sheet. (You can also steam or boil the corn if you don't have a grill. See instructions below in the Notes section.)
In a small bowl, add mayonnaise and lime juice. Mix together with a spoon.
Using a brush or a butter knife, spread the mayonnaise mixture onto each ear of grilled corn.
Sprinkle each ear with 2 tablespoons of Cotija cheese, 1 tablespoon of cilantro and a pinch of chili powder. Taste and season with salt if desired.
To steam the corn, add 2-3 inches of water into a large pot and then insert a steamer rack. Make sure the water isn't touching the rack. Cover and bring the water to a boil. Placed the shucked ears of corn in the steamer rack, cover and steam for about 5-7 minutes, until the corn turns a beautiful golden yellow and is tender but still crisp. Remove from the rack and continue to step 3 of the recipe.To boil the corn, fill a large pot or Dutch oven halfway with water. Bring to a boil. Add in the shucked ears of corn, cover and bring to a boil again. Cook for about 5-6 minutes, until the corn turns a beautiful golden yellow and is tender but still crisp. Remove from the pot and continue to step 3 of the recipe.To grill the corn with the husk on, just leave the husk undisturbed while it’s on the grill to help the corn steam. Cook for about 10 minutes, turning frequently, until the husks become charred and the corn is tender.Try using a brush instead of a butter knife to spread the mayo and lime juice mixture onto the corn. It will help evenly cover the surface.If you’re making this for kids (or others) who might have trouble eating off a cob, slice the kernels off the cob into a bowl with a knife. Then mix in all of the remaining ingredients.