Combine Sauce Ingredients: In the removable insert of a 3-quart or larger slow cooker, pour in the beef broth and low-sodium soy sauce. Add the brown sugar substitute, sesame oil, minced garlic, and minced ginger. Whisk thoroughly until all sauce components are well blended.
Add and Coat Beef: Introduce the thinly sliced beef to the sauce in the slow cooker. Stir gently to ensure each piece of beef is fully coated with the marinade.
Slow Cook the Beef: Place the lid securely on the slow cooker. Set the appliance to the LOW heat setting and allow the beef to cook for 4 to 5 hours. The beef should be fork-tender when done. Note that cooking duration can vary slightly based on your slow cooker model and beef thickness.
Prepare Thickener and Add Broccoli: Approximately 30 minutes before the beef's cooking cycle is finished, create the cornstarch slurry. In a small bowl, combine the cornstarch with the cold water, whisking until completely smooth and free of lumps.
Thicken Sauce and Cook Broccoli: Pour the prepared cornstarch slurry into the slow cooker, stirring it gently into the beef and sauce. Distribute the frozen broccoli florets evenly over the beef. Replace the lid and continue to cook on LOW for an additional 30 minutes. This period allows the broccoli to cook to a tender-crisp texture while the sauce thickens.
Serve and Enjoy: After the final 30 minutes, the broccoli will be vibrant and the sauce lusciously thickened. Turn off the slow cooker. Serve your Easy Crock-Pot Beef & Broccoli hot. For a complete low-carb meal, pair it with cauliflower rice, shirataki noodles, or your favorite steamed non-starchy vegetables.