Preheat the oven to 400 degrees . In a shallow bowl, whisk together the corn chips, 2 teaspoons chili powder, 1 teaspoon salt and 1/4 teaspoon pepper. Add the flour to another shallow bowl. In a third shallow bowl, beat the eggs.
Spray a baking sheet with cooking spray. Season the chicken with salt and 1/2 teaspoon chili powder, then coat with the flour. Dip in the eggs, coat with the chip mixture and arrange on the prepared baking sheet. Bake until golden, about 20 minutes. Top with the cheese and bake until melted, about 4 minutes.
In a saucepan, combine the black beans, remaining 2 teaspoons chili powder and 1/4 cup sour cream. Cook, mashing, over medium heat until heated through; season with salt.
On a platter, top the chicken with the beans, remaining sour cream, tomatoes and scallions.