Pat dry the sliced beef strips with paper towels and toss with ½ teaspoon salt. Set aside. In the slow cooker, combine all sauce ingredients and whisk until the cornstarch dissolves. Add the beef to the sauce and stir to combine.
Cover and cook on LOW for 3-4 hours until the beef is tender. Once the beef is tender, tilt the slow cooker to the side and transfer as much sauce as possible into a saucepan using an oven mitt. Set aside.
Add broccoli on top of the beef in the slow cooker, covering it without stirring to allow the broccoli to steam. Cook for an additional 20-30 minutes until the broccoli is crisp-tender.
Meanwhile, simmer the sauce on the stove until thickened to a desired consistency. Transfer the thickened sauce back to the slow cooker and stir to combine with the beef and broccoli.
Serve with rice and garnish with sesame seeds and green onions if desired. Enjoy!