Combine the beef chuck, peppercorns, ginger, water, garlic powder, and onion in a slow cooker.
Cover the slow cooker and start to slow cook in high for 8 to 10 hours.
Put-in the scallions and fish sauce. Stir and continue to slow cook for 30 minutes.
Transfer to a serving bowl. Serve with a small bowl of fish sauce and lemon along with some chili flakes.
Share and enjoy!