Preheat oven to 250 degrees. Split hoagie rolls down the center then set aside. Tear 4 large sheets of foil then set aside.
Heat a large skillet over medium-high heat then add butter. Add onions then saute until golden brown, about 3 minutes. Add chicken, season with salt and pepper, and then saute until no longer pink. Add buffalo wing sauce then stir to combine.
Separate mixture into 4 piles then top with cheese slices. Cover with a lid to melt cheese then remove skillet from heat. Scoop each cheese-topped pile into a split hoagie roll then wrap tightly in foil. Place into the oven to warm completely through for 10 minutes. Unwrap then serve.
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