In a large skillet, heat the vegetable oil over medium-high heat. Season the beef cubes with salt and pepper, then add them to the skillet. Sear the beef on all sides until browned, about 5-7 minutes. Remove from heat and set aside.
In a slow cooker, combine the sesame oil, minced garlic, minced ginger, soy sauce, brown sugar, and rice vinegar. Stir well to combine.
Add the seared beef to the slow cooker and stir to coat the beef in the sauce.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the beef is tender and easily shredded with a fork.
Once cooked, sprinkle sesame seeds over the beef and stir gently.
Serve hot, garnished with sliced green onions.