1. Mix the red wine vinegar, ketchup, soy sauce and garlic powder together in a resealable plastic bag. Add the steak, close the bag, squeezing out the air, and marinate 20 minutes at room temperature
2. Preheat the grill to medium-high. Spray the grill well with non-stick cooking spray, then lift the steak out of its marinade and grill, turning once, 3 to 5 minutes per side for medium-rare
3. Let the steak rest for at least 5 minutes, then slice it thinly across the grain. Serve hot, room temperature or cold, sprinkled with flaky salt and pepper
4. Marinate the steak in the fridge for up to 24 hours.

  Preparation: 5min