Divide each onion wedge into 2 equal pieces. Thread 3 okra pods, 2 cherry tomatoes, and 2 onion pieces alternately onto each of 8 (12-inch) skewers. Combine olive oil, kosher salt, and the remaining ingredients except for cooking spray in a small bowl, stirring with a whisk. Brush olive oil mixture over the skewers. Place the skewers on a grill rack coated with cooking spray, and grill skewers for 3 minutes on each side or until tender.