INGREDIENTS For the Marinade: 1/3 cup balsamic vinegar 1/3 cup Worcestershire sauce 1/3 cup olive oil 2 garlic cloves, grated 1/2 tsp. ground black pepper 1/4 tsp. red pepper flakes (optional) 2 Tbsp. honey, divided 2 Tbsp. Dijon mustard, divided For the Kebabs: 1 1/2 lbs sirloin or New York strip, cut into 1-inch cubes 8 oz. 1 baby portobello mushrooms, large stems removed 1 red onion, cut into 1-inch pieces 1 green bell pepper, cut into 1-inch pieces 1 yellow bell pepper, cut into 1-inch pieces 1 red bell pepper, cut into 1-inch pieces Chopped fresh parsley, for garnish INSTRUCTIONS For the marinade: Whisk together the vinegar, Worcestershire, olive oil, garlic, black pepper, red pepper flakes, and 1 tablespoon each of the honey and mustard in a medium bowl. Transfer 1/4 cup of the marinade to a small bowl; whisk in the remaining 1 tablespoon each honey and mustard to make a glaze. Set the glaze aside. For the kebabs: Add the marinade and the meat to a resealable plastic bag. Seal the bag and massage it gently to coat all of the meat. Refrigerate at least 1 hour or up to 6 hours. Remove the meat from the refrigerator 30 minutes before grilling. If using wooden skewers, soak in water for at least 30 minutes. Preheat the grill to medium-high heat (400 to 450°). Thread the meat, mushrooms, onion, and peppers on the skewers, alternating as you like. Grill the kebabs uncovered until grill marks form, about 4 minutes. Turn the kebabs, and brush the grilled side with half of the glaze. Continue grilling until grill marks form on the bottom side, 3 to 4 minutes more. Turn the kebabs, and brush with the remaining glaze; grill to desired degree of doneness (about 135° for medium), about 1 minute more. Let kebabs rest for 5 minutes. Sprinkle with parsley just before serving.