In a medium bowl, combine the chopped parsley, minced garlic, red wine vinegar, red pepper flakes, and salt and pepper for the chimichurri sauce.

Slowly whisk in the olive oil until the sauce is combined.

Season the flank steak generously with salt and pepper on both sides.

In a large skillet or grill pan, add the olive oil and heat over medium-high heat.

Once the pan is sizzling, add the flank steak and cook for about 4-5 minutes on each side for medium-rare.

Transfer the steak to a cutting board and let it rest for 5 minutes.

Slice the flank steak against the grain for maximum tenderness.

Drizzle the chimichurri sauce generously over the sliced steak and serve it hot.