Preheat the oven to 375°F (190°C).
Prepare the bell peppers by cutting them in half lengthwise and removing the seeds.
In a large bowl, combine shredded chicken, buffalo sauce, cream cheese, half the cheddar cheese, green onions, garlic powder, salt, and pepper.
Scoop the buffalo chicken mixture into each pepper half, packing it tightly.
Place the stuffed peppers in a baking dish and sprinkle the remaining cheddar cheese on top.
Cover the dish with aluminum foil and bake for 25 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden brown.