Season the flank steak generously with salt and crushed black peppercorns on both sides.
Heat olive oil in a skillet over medium-high heat.
Add the seasoned steak to the skillet and sear for 4-5 minutes on each side.
Remove the steak from the skillet and let it rest.
In the same skillet, add minced garlic and sauté for 30 seconds.
Pour in the beef broth, scraping up browned bits.
Add soy sauce and Dijon mustard, stirring to combine.
Let the sauce simmer for 5-7 minutes until thickened.
Slice the rested steak against the grain into thin strips.
Serve the steak topped with the peppercorn sauce and garnish with parsley.