1 1/2 lb boneless top sirloin steak, trimmed of visible fat and cut into 2-inch chunks 2 large cloves garlic, chopped 2 tablespoon chopped fresh rosemary 1 tablespoon red wine vinegar 1 tablespoon low-sodium soy sauce 1/2 tablespoon olive oil 3/4 teaspoon fresh ground black pepper, divided 1 large red onion, quartered and layers separated 1 each large red, yellow and green bell pepper, cut into 1 1/2-inch chunks 1/2 teaspoon sea salt High-heat cooking oil (such as sunflower, safflower, peanut or grape seed oil), as needed

1. In an 8 or 9-inch square baking dish, combine sirloin, garlic, rosemary, vinegar, soy sauce, olive oil and 1/2 teaspoon black pepper. Stir gently to coat. Cover and refrigerate for 60 to 24 hours, stirring 2 or 3 times.
2. Thread skewers, alternating between sirloin, onion and bell pepper. Sprinkle with salt and remaining 1/4 teaspoon black pepper.
3. Heat a grill on medium-high. Lightly brush grate with cooking oil and transfer skewers to grill. Cook, turning once or twice, until sirloin reaches desired doneness, 9-11 minutes for medium-rare to medium or 11-13 minutes for medium to medium-well. Transfer to a large plate and let rest for 5 minutes.