In a large skillet, cook beef, pepper and onion over medium heat until meat is no longer pink, 8-10 minutes, breaking up beef into crumbles; drain. Stir in ketchup, sloppy joe mix, brown sugar and mustard.
Transfer to a 3-qt. slow cooker. Cover and cook on low until flavors are blended, 4-5 hours. Serve on buns.
Slow-Cooker Sloppy Joes Tips
Can you use ground turkey instead of ground beef?
For a healthier spin, you can make slow-cooker turkey sloppy joes instead. However, you'll get the most flavor with quality ground beef that has about 20% fat.
How else can you cook sloppy joes?
To speed up the preparation, cook the mixture on the stovetop instead of transferring it to a slow cooker. Simmer the meat mixture over medium heat for about 15 minutes, or until heated through.