In a medium bowl, whisk together 4 tablespoons olive oil, balsamic vinegar, lemon juice, Dijon, brown sugar, Worcestershire, garlic and Italian seasoning; season with salt and pepper, to taste. Reserve 1/3 cup and set aside.
In a gallon size Ziploc bag or large bowl, combine chicken and olive oil mixture; marinate for at least 1 hour to 4 hours, turning the bag occasionally. Drain the chicken from the marinade.
Thread chicken, zucchini, bell peppers, and onion onto skewers. Brush with remaining 2 tablespoons olive oil; season with salt and pepper, to taste.
Preheat grill to medium heat.
Add skewers to grill, and cook, turning occasionally, until the chicken is completely cooked through, reaching an internal temperature of 165 degrees F, about 10 minutes. Brush skewers with reserved olive oil mixture, cooking for an additional 1-2 minutes.
Serve immediately, garnished with parsley, if desired.
Notes
An outdoor grill is not necessary. Too cold to grill outside? A cast iron grill pan can be used to get those favorited grill marks and charred flavor.
Cut in uniform size. Cut all of the kabob ingredients in similar size pieces for even cooking and a consistent bite.
Use different veggies. Mix it up and add in cherry tomatoes, mushrooms, summer squash or baby potatoes (par cooked beforehand).
Choose the right skewers. Metal skewers are more durable and can be reused, but will retain heat, requiring caution when handling. Wooden skewers are budget-friendly and disposable for easy clean-up, but will need to be soaked (to prevent burning) beforehand.
Soak and freeze wooden skewers at the start of summer. Soak the skewers for at least 30 minutes (warm or cold water). Drain and store in a freezer bag for later use, using them straight from the freezer all season long.
Start with a hot grill (or hot pan). A hot, clean grill prevents sticking and helps achieve that favorited sear and caramelized crust.
Work in batches. An overcrowded grill or pan can lead to uneven cooking and poor browning. Work in batches to maintain high heat for a good sear and crispy crust on each chicken skewer.
Use an instant-read thermometer for the most accurate results. The internal temperature should reach 165°F.
Let your meat rest. Let your chicken kabob rest for at least 5 minutes prior to serving, allowing the juices to redistribute – this will allow for maximum flavor and juiciness.
Reheat in the oven. Leftover chicken can be rubbery when reheated. For best results with leftovers, reheat in the oven at 350°F, covered in aluminum foil until warmed through.