In a medium bowl combine soy sauce, rice wine vinegar, brown sugar, sesame oil, ginger, and garlic. Mix well to combine and set aside.
In a skillet over medium heat, add ground beef and onion and cook until browned (about 5 minutes). The meat will still be a little pink.
Add the Bulgogi sauce and mix well. Simmer for 6-10 more minutes, and remove from heat.
Evenly distribute the mixture between 4 bowls. Top with scallion, sesame seeds, and a soft boiled egg.
Serve over rice.
