Season the chicken breasts with salt, pepper, and chili powder.
Heat olive oil in a skillet over medium heat and cook chicken until golden brown and fully cooked, about 6–7 minutes per side.
Let the chicken rest for a few minutes, then slice into strips.
In a bowl, stir together sour cream (or Greek yogurt), lime juice, and a pinch of chili powder for the sauce.
Assemble bowls with a base of cooked brown rice. Top with sliced chicken, corn, black beans, and diced red bell pepper.
Drizzle with the sauce, sprinkle with cotija cheese and fresh cilantro, then serve.