Whisk together soy sauce, brown sugar, sesame oil, rice vinegar, minced garlic, grated ginger, and chili flakes in a bowl. Toss the sliced beef in the mixture and let it marinate for 15 minutes.

Transfer the marinated beef to the slow cooker. Sprinkle toasted sesame seeds and sliced green onion on top.

Cook on low for 7 hours (420 minutes).

While the beef cooks, rinse jasmine rice under cold water until the water runs clear. In a pot, combine rice, water, and a pinch of salt. Bring to a boil, then reduce heat, cover, and simmer for 18 minutes until the water is absorbed.

When the beef is done, stir it to redistribute the juices. Serve the bulgogi over the cooked rice, drizzle with a little extra sesame oil if desired, and before serving, verify doneness with a food thermometer.