In a large pot, bring salted water to a rolling boil over high heat. Add the fresh corn kernels and cook for 5-7 minutes until they are tender yet still crisp. Once cooked, drain the corn in a colander and set it aside to cool.

While the corn is cooling, chop the medium cucumber into bite-sized pieces, halve the cherry tomatoes, and finely dice the red onion. Combine these ingredients including the cooled corn in a large mixing bowl.

In a medium-sized bowl, whisk together the mayonnaise and sour cream until smooth and creamy. Squeeze in the lime juice, then sprinkle in the chili powder along with salt and pepper to taste. Mix until well combined.

Pour the creamy dressing over the mixture of corn and veggies. Gently toss everything together until evenly coated with the dressing.

Crumble the feta cheese over the top and sprinkle with fresh cilantro if desired. Serve immediately or refrigerate for up to an hour to let the flavors meld.