Place chicken breasts in the bottom of the slow cooker.
Pour the sloppy joe sauce on top and place onions and green peppers on top.
Place the lid on top of the slow cooker and cook on low heat for 5-6 hours (chicken breasts tend to dry out quickly, so start checking it around 5 hours to see if it's done) or high heat for 3-4 hours.
Remove chicken from slow cooker and shred using 2 forks (it should fall apart fairly easily). Place shredded chicken back in the Instant Pot with all the juices and stir together. Add salt and pepper as needed.
Scoop onto hamburger buns and serve topped with your favorite fixings (we love shredded lettuce, dill pickles, and sliced tomatoes).
Notes
To turn this into a freezer meal:
Place chicken breasts, sloppy joe sauce, onions, and green peppers into a gallon-sized freezer bag. Place freezer bag into freezer and it will last up to 90 days.
When ready to use, dump ingredients from bag into slow cooker. Place the lid on top and cook on LOW for 5-6 hours or until chicken is completely cooked through. Follow the rest of the instructions as written.