In a large skillet, heat the oil and add the chicken, onion, and green pepper. Season with salt and brown the chicken and the vegetables for about 5 minutes, or until the chicken is no longer pink and lightly browned.
Transfer the mixture to the slow cooker.
Make a cornstarch slurry by combining cornstarch with chicken stock and Worcestershire sauce in a bowl, then pour that into the slow cooker over the chicken mixture and stir to combine.
Cook on LOW covered with a lid for 4 hours or on high for 1 ½ to 2 hours.
Remove the lid, and add slices of provolone cheese on top of the sloppy joe mixture. Cover with the lid and allow to melt for about 10 minutes.
Stir to combine, then serve in warmed up or toasted hamburger buns.
Notes
Substitute ground chicken for your favorite ground protein (beef, pork, or turkey).
You can brown the meat, onions and peppers beforehand and freeze for when you are ready to throw everything in the slow cooker.
You can add mushrooms if you like.
Frozen peppers and onions are a quick way to make this faster.
You can use any cheese you like, American cheese, shredded or sliced mozzarella or even cheez-whiz.
I love using brioche buns, hamburger buns, or onion buns but this would also be great in a sub bun.