For the sauce:
In a large bowl, mix together all the sauce ingredients and stir well to combine.
Place the beef in the slow cooker and cover with the sauce mixture. Place the lid on the slow cooker and cook on a low heat for 8 hours or on a high heat for 4 hours.
Once the beef has finished cooking, mix the cornstarch and ¼ cup water and stir into the slow cooker to thicken the sauce.
Cover and cook on high heat for another 30 minutes, or until the sauce has thickened.
Serve immediately, garnished with green onions and sesame seeds.
Serving suggestion: