Pat the chicken breasts dry and season lightly with salt, pepper, and chili powder. Heat grill or skillet over medium-high and cook chicken until 165°F (about 6–8 minutes per side). Let rest, then slice into strips.
In a small bowl, mix sour cream or Greek yogurt, lime juice, garlic powder, and 1/4 teaspoon salt for the lime crema. Adjust to taste.
Heat a skillet over medium heat, add olive oil, then add corn kernels. Sauté for 3–4 minutes until lightly charred. Stir occasionally. Add chili powder, smoked paprika, cumin, 1/4 teaspoon salt, and black pepper. Toss well.
Warm the rice in a pan or microwave if needed. Briefly warm the black beans if desired and slice the rested chicken.
Assemble the bowls: start with rice, layer chicken, charred corn, black beans, tomatoes, red onion, and cotija cheese. Drizzle lime crema and garnish with cilantro. Serve immediately.
Notes
For best texture, keep wet ingredients separate until serving. Adjust the creaminess of lime crema to your liking.