Whisk the soy sauce, gochujang, honey, garlic, ginger, and sesame oil in a mixing bowl until smooth.
Spread the sliced onion evenly across the bottom of the slow cooker.
Place the beef short ribs on top of the onion in a single layer.
Pour the sauce mixture and beef broth over the ribs.
Cover and cook on low for 8 hours until the meat is very tender and pulls away from the bone easily.
Skim off any visible fat from the surface. Serve the ribs with the sauce spooned over the top and finish with green onions and sesame seeds.