01 -
Slice the flank steak into thin strips. Place the beef strips and cornstarch into a large resealable plastic bag, seal securely, and shake until the steak pieces are evenly coated.
02 -
Pour the sesame oil, minced garlic, soy sauce, beef broth, brown sugar, chopped onion, and red pepper flakes into the slow cooker. Stir gently to blend all ingredients together.
03 -
Transfer the coated flank steak into the slow cooker and stir until each piece is thoroughly coated in the sauce mixture.
04 -
Cover and cook on high for 2 to 3 hours or on low for 4 to 5 hours, until the beef is fully cooked and tender.
05 -
Portion the beef onto serving plates or over hot cooked rice if desired, and garnish with sesame seeds and chopped green onions.