In a bowl, stir together the gochujang, soy sauce, honey, garlic, ginger, and beef broth until smooth.
Place the short ribs and sliced onion in the slow cooker. Pour the sauce over the top and turn the ribs to coat.
Cover and cook on low for 8 hours until the meat is very tender.
About 30 minutes before serving, cook the rice according to package directions.
While the rice cooks, combine the cucumber, carrots, rice vinegar, sugar, and salt in a bowl. Stir and let the vegetables sit for at least 15 minutes.
Remove the ribs from the slow cooker and serve them over the rice with a spoonful of the pickled vegetables on the side.
Sprinkle each plate with sliced green onions and sesame seeds before eating.