Coarsely chop half of the cilantro stems and leaves; reserve remaining cilantro for step 6. Finely chop ½ teaspoon garlic. Finely grate all of the lime zest and squeeze juice from half of the lime into a medium bowl; cut remaining lime into wedges. Stir in chopped cilantro and garlic, 2 tablespoons oil, 1 teaspoon chili powder, ½ teaspoon salt, and a few grinds of pepper.
2. Prep chicken & make crema
In a small bowl, whisk to combine mayonnaise and 1 tablespoon of the lime marinade. Season to taste with salt and pepper; set aside for step 6. Pat chicken dry, transfer to bowl with remaining marinade, and turn to coat.
3. Cook chicken & corn
4. Cut corn & shred chicken
Once corn and chicken have cooled slightly, use a sharp knife to carefully remove kernels from corn cob. Use your hands to coarsely shred chicken (or thinly slice with a knife).
5. Heat tortillas
Place tortillas directly on skillet and heat until lightly browned and warmed through, 1–2 minutes (watch closely).
6. Finish & serve
Thinly slice radishes. Spread crema on tortillas, then top with corn and shredded chicken. Tear remaining cilantro leaves and stems over and top with radish slices. Sprinkle with crumbled feta and chili powder, if desired. Serve chicken tacos with lime wedges on the side for squeezing on top. Enjoy!