Arrange a rack in the middle of the oven and heat the oven to 425F.
In a skillet, heat olive oil over medium heat. Season chicken with salt and pepper. Cook in the skillet for about 6 minutes on each side, until it's browned and cooked through. Set aside to cool.
In a 9x13-inch baking dish add white onion, black beans, corn kernels, diced tomatoes and their juices, and diced green chiles (do not drain). Next add chili powder, paprika, garlic powder, ground cumin, and kosher salt.
Chop cooled chicken into bite-sized pieces and add to the baking dish. Stir to combine. Pour in chicken broth.
Bake until the mixture is heated through, about 40 minutes. Meanwhile, thinly slice scallions and coarsely chop fresh cilantro.
Sprinkle the casserole with 2 cups shredded Mexican blend cheese and bake until melted, about 5 minutes. Let cool for at least 15 minutes before serving. Sprinkle with the scallions and cilantro before serving. Serve over rice.