Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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.

Step 5

Let kebabs rest for 5 minutes. Sprinkle with parsley just before serving.