Preheat a grill or grill pan over medium-high heat.
In a small bowl, combine chili powder, ground cumin, garlic powder, salt, and black pepper.
Rub the chicken breasts with olive oil and then evenly coat with the spice mixture.
Grill the chicken breasts for 6-7 minutes per side or until fully cooked and internal temperature reaches 165°F (74°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 large mixing bowl.
In a separate small bowl, whisk together mayonnaise, sour cream, lime juice, smoked paprika, and a pinch of salt.
Add the dressing to the bowl with the corn kernels and stir to combine.
Dice the rested chicken breasts into bite-sized pieces and add to the corn mixture.
Add crumbled cotija cheese, chopped cilantro, red onion, jalapeño, chopped romaine lettuce, and diced tomato to the bowl.
Gently toss all ingredients together until well combined.
Taste and adjust seasoning with additional salt or lime juice if desired.
Serve the Street Corn Chicken Salad immediately or chill for 30 minutes before serving for a cooler salad.