Preheat a grill to medium. Add the corn and grill until charred in spots, about 10 minutes. Let cool completely.
In a large bowl, whisk together the EVOO, lime juice, chili powder and 1/2 teaspoon salt. Using a large, sharp knife, carefully cut the corn kernels from the cobs and transfer to the bowl. Add the beans, radishes, scallions and cilantro; toss well. Divide the salad among 4 plates; top with the queso and avocado.