Slice the chicken breasts into small, bite-sized cubes.

In a reusable container, vigorously whisk together the olive oil, soy sauce, lemon juice, brown sugar, balsamic vinegar, minced garlic, and black pepper to form the marinade. Introduce the cubed chicken into the marinade, stir thoroughly, and cover. Refrigerate for a duration of 30 minutes up to 24 hours.

Once marinated, heat the grill to a medium setting.

Assemble the kabobs by threading the marinated chicken cubes and chopped vegetables onto metal skewers, alternating between pieces of red onion, red bell pepper, chicken, orange bell pepper, and zucchini, repeating until the skewers are full. Aim to place approximately five chicken pieces on each skewer.

Arrange the kabobs onto the heated grill and cook for 5 to 6 minutes. Carefully flip them using tongs and grill for an additional 5 to 6 minutes or until an instant-read thermometer inserted into the thickest piece of chicken reads 165°F, avoiding skewers to ensure an accurate reading.

Withdraw the kabobs from the grill and, if using metal skewers, allow them to cool briefly before handling. Serve and enjoy!