In a small bowl, whisk together the beef broth, soy sauce, Worcestershire sauce, olive oil, brown sugar, minced garlic, onion powder, smoked paprika, salt, and pepper to create the marinade.
Place the flank steak in the slow cooker.
Pour the marinade over the flank steak, making sure it's evenly coated.
Cover the slow cooker and cook on low for 6-8 hours, until the flank steak is tender.
Once done, remove the flank steak from the slow cooker and let it rest on a cutting board for 5-10 minutes.
Slice the flank steak against the grain into thin strips.
Notes
If you prefer, you can cook on HIGH for 3-4 hours, but the meat won’t be as tender.If you want a thicker sauce, just create a slurry: Remove the flank steak from the slow cooker once it's done cooking, and then whisk together 2 tablespoons of cornstarch with 2 tablespoons of cold water. Stir this mixture into the slow cooker and cook on high for an additional 15-20 minutes, or until the sauce has thickened.Refrigerate any leftovers in an airtight container for up to 5 days.