In a medium bowl, whisk together soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, and crushed red pepper flakes until sugar is dissolved.
Heat a large skillet over medium-high heat. Add ground beef and cook, breaking it apart with a spatula, until browned and cooked through, about 5-7 minutes.
Drain excess fat from the skillet if necessary.
Pour the soy sauce mixture over the cooked ground beef. Stir well to combine and cook for an additional 2-3 minutes until the sauce thickens slightly and coats the beef evenly.
Divide the cooked white rice evenly among four bowls.
Top each bowl of rice with the Korean ground beef mixture.
Garnish each bowl with sliced green onions and toasted sesame seeds.
Serve immediately.