Preheat your oven to 375°F (190°C). Lightly grease a baking dish.
Slice each bell pepper in half lengthwise and remove the seeds and membranes. Place them cut-side up in the baking dish.
In a large bowl, mix together shredded chicken, cream cheese, buffalo sauce, ranch (or blue cheese dressing), cheddar cheese, mozzarella, and green onions. Season with salt and pepper to taste.
Fill each pepper half with the buffalo chicken mixture, pressing it in slightly to pack well.
Bake uncovered for 25–30 minutes, until the peppers are tender and the filling is hot and bubbly. If desired, broil the last 2 minutes to lightly brown the top.
Top with chopped green onion, blue cheese crumbles, or a drizzle of extra buffalo sauce. Serve hot!