In a medium bowl, whisk together olive oil, soy sauce, balsamic vinegar, lemon juice, and brown sugar. Add Dijon mustard and seasonings.

Reserve 3 tablespoons of the marinade for basting. Combine remaining marinade with chopped zucchini, bell peppers, and red onion in a large bowl.

Cut chicken into uniform cubes and add to reserved marinade. Cover and refrigerate for at least 4 hours.

Soak wooden skewers in water for at least 30 minutes.

Assemble kabobs by alternating marinated chicken and vegetables on skewers.

Preheat grill to medium-high heat and grill kabobs for 8-12 minutes.