In a mixing bowl, combine the soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, black pepper, and red pepper flakes.

Whisk the mixture until the sugar dissolves completely.

Thinly slice your beef against the grain.

Place the sliced beef into the marinade and use your hands to coat it evenly.

Cover the bowl with plastic wrap or transfer the beef to a zip-top bag and let it marinate in the refrigerator for at least 30 minutes or up to 24 hours.

Preheat your grill or stovetop pan over medium-high heat.

Remove the beef from the marinade and grill or cook in the pan for about 2-3 minutes per side.

Once cooked, remove the beef from the heat and let it rest for a few minutes.