If using fresh corn, boil the corn cobs for 5-7 minutes until tender, then let them cool. If using frozen corn, simply thaw and drain any excess water.
Once cooled, cut the kernels off the cob and place them in a large mixing bowl.
Add the diced red bell pepper, green bell pepper, finely chopped red onion, cherry tomatoes, and diced avocado to the bowl with the corn.
In a separate small bowl, whisk together the mayonnaise, lime juice, chili powder, salt, and pepper until well combined.
Pour the dressing over the corn and vegetable mixture, then gently toss until all the ingredients are evenly coated.
Fold in the crumbled feta cheese and fresh cilantro gently to avoid mashing the avocado.
Taste and adjust seasoning if necessary, adding more lime juice, salt, or pepper as desired.