This Grilled Balsamic Marinated Flank Steak recipe is easy, tender and juicy with a sweet heat that's to die for. It's the best flank steak recipe ever!
In a large measuring cup or bowl, add vinegar, soy sauce, brown sugar, garlic, red pepper flakes, mustard and green onions. Stir to combine.
Pierce a flank steak all over with a fork. Place in a large gallon size Ziplock bag and pour in the marinade. Squeeze as much air as possible out of the bag and seal. Massage the marinade into the meat, then place in refrigerator for 6 hours or up to overnight.
Heat a grill over high heat. Add the steak to the grill and reduce grill temperature to medium and cook for approximately 5 minutes. Flip and cook until internal temperature reaches 145 F for medium rare. Remove from grill to cutting board, tent with foil, and allow to rest for at least 10 minutes.
Slice the steak on a double bias to achieve the most tender texture and serve immediately.