Cook the ground beef and onion in a skillet on medium heat until the beef is browned. Drain the grease.

Add the beef and onion mixture to your slow cooker.

Mix together remaining ingredients, except for diced tomatoes, in a small bowl.

Add the sauce and the diced tomatoes to the beef in the slow cooker.

Put on lid and cook in slow cooker for 3 hours on low. Serve on buns.