In a resealable bag, combine flank steak, half of the olive oil, salt, and pepper. Let it marinate for at least one hour or overnight for best results.

Blend parsley, garlic, remaining olive oil, red wine vinegar, salt, and red pepper flakes until smooth but slightly chunky to prepare the chimichurri sauce.

Preheat your grill to medium-high (around 450°F).

Remove the steak from the marinade and grill for about 5-7 minutes per side for medium-rare.

Allow the steak to rest for 5 minutes before slicing it against the grain.

Drizzle the chimichurri sauce over the sliced steak and serve.