Preheat the oven to 400°F. Spray a 9x13-inch baking dish with nonstick cooking spray.
Cut the poblano peppers in half lengthwise. Remove the seeds and membranes.
In a large mixing bowl, combine the cooked chicken, 1 cup Monterey Jack cheese, half of the sliced green onions, black beans, diced tomatoes, corn, garlic powder, chili powder, cumin, salt, and black pepper.
Spoon the chicken mixture evenly into the poblano pepper halves. Arrange the stuffed peppers in the prepared baking dish.
Bake for 15 minutes, or until the peppers begin to soften.
Sprinkle the remaining ½ cup Monterey Jack cheese and green onions over the peppers. Bake for an additional 5 minutes, or until the cheese is melted.
Remove from the oven and let the peppers rest for 10–15 minutes before serving.
Notes
Refrigerate leftovers in an airtight container for up to 5 days.