Remove flank steak from the refrigerator and allow it to come to room temperature.
In a bowl, mix olive oil, minced garlic, soy sauce, balsamic vinegar, black pepper, and chopped rosemary.
Place the flank steak in a ziplock bag and pour the marinade over it.
Seal the bag and refrigerate for at least 2 hours or overnight.
Preheat the grill or skillet over medium-high heat.
Remove the steak from the marinade and let excess liquid drip off.
Season the steak with salt on both sides.
Place the steak on the grill or skillet and cook for about 4-5 minutes per side.
Use a meat thermometer to check for an internal temperature of 130-135°F.
Remove the steak from heat, cover it with foil, and let it rest for 10 minutes.
Slice against the grain and garnish with fresh parsley before serving.