Preheat your grill to medium-high. Grill the corn on the cob for about 10-15 minutes, turning every few minutes until the kernels are slightly charred and cooked. Remove from the grill and let cool.
Once cooled, carefully slice the kernels off the cob and place them in a large mixing bowl.
Add the diced red bell pepper, chopped red onion, and diced avocado to the bowl with the corn.
In a separate small bowl, whisk together the mayonnaise, lime juice, chili powder, and a pinch of salt and pepper until smooth.
Pour the dressing over the corn mixture and gently toss everything together to combine.
Fold in the crumbled cotija cheese and chopped cilantro until evenly distributed.
Taste the salad and adjust seasoning with more salt, pepper, or lime juice as needed.
Let the salad sit in the refrigerator for at least 30 minutes before serving to let the flavors meld.