Mediterranean Chicken Kebabs

Ingredients

• 12 (10-inch) wooden skewers
• 1/2 cup balsamic vinegar
• 2 tablespoons olive oil
• 1 tablespoon honey
• 2 garlic cloves, minced
• 1/2 teaspoon salt
• 1 large red onion, halved
• 1 1/2 pounds skinless, boneless chicken thighs, cut into 2-inch pieces
• 2 large zucchini, cut into 1-inch slices
• Cooking spray