Chopped green onions and toasted sesame seeds optional for serving
Coat a 4-quart or larger slow cooker with nonstick spray. Place the beef in the bottom.
In a small bowl, stir together the beef broth, soy sauce, oyster sauce, honey, rice vinegar, chili-garlic paste, and garlic.
Pour over the beef, then stir to combine. Cover and cook on LOW for 1 1/2 hours.
In a small bowl, whisk together 1/4 cup of water and cornstarch. Stir into the slow cooker with the beef and sauce, then place the broccoli on top.
Cover, turn the heat to HIGH, and cook another 30 minutes until the broccoli is tender. Serve warm over rice, sprinkled with green onions and sesame seeds as desired.
TO STORE: Keep leftovers in the refrigerator for up to 4 days.
TO REHEAT: Warm gently in the microwave or on the stovetop with a splash of beef broth or water to keep it from drying out.
TO FREEZE: Store in an airtight container for up to 2 months in the freezer. Defrost overnight in the refrigerator before warming.
DOUBLE BATCH: I have not tried doubling this recipe, but I think that you could easily do about 1.5 times the amount. Watch the cooking time, as it may need to be adjusted slightly.
COOKING TIP: Because flank steak is fairly lean, I would not recommend leaving the slow cooker on low longer than the recipe specifies, or I worry it might overcook. If you have a programmable slow cooker that switches to keep warm, this might be an option, but the best choice is to be able to check it right away at the 1 1/2 hour mark.