Add the beef and stir-fry until well browned. Push the beef to one side of the skillet. Add the broccoli, onion and garlic to the other side of the skillet and stir-fry until tender-crisp.

Uncover the slow cooker and stir well to break up any clumps of beef, but not shred the meat. Stir in the cornstarch mixture, then stir in the broccoli. Cover and cook on low until the broccoli is ...