Preheat a grill or grill pan over medium-high heat.
In a small bowl, mix olive oil, chili powder, cumin, garlic powder, salt, and black pepper.
Brush the chicken breasts with the spice mixture on both sides.
Grill the chicken breasts for 6-7 minutes per side or until fully cooked and internal temperature reaches 165°F (75°C). Remove from grill and let rest for 5 minutes.
While the chicken cooks, grill the corn ears, turning occasionally, until charred in spots, about 8-10 minutes. Remove from grill and let cool slightly.
Cut the kernels off the corn cobs and place them in a medium bowl.
Add mayonnaise, lime juice, smoked paprika, cayenne pepper, and a pinch of salt to the corn kernels. Stir to combine well.
Slice the rested chicken breasts into thin strips.
In a large salad bowl, combine chopped romaine lettuce, cherry tomatoes, sliced red onion, and half of the corn mixture. Toss gently to combine.
Divide the salad onto four plates or bowls.
Top each salad with sliced grilled chicken, the remaining corn mixture, crumbled cotija cheese, and chopped cilantro.
Serve immediately.