Preheat the grill to medium-high heat. If using wooden skewers, soak them in water for at least 30 minutes to prevent burning.
In a large bowl, combine olive oil, soy sauce, honey, garlic powder, onion powder, smoked paprika, salt, and pepper. Divide the marinade into three separate bowls.
Add the chicken cubes to one bowl and toss to coat. Add the shrimp to the second bowl and toss with lemon juice and Old Bay seasoning. In the third bowl, add the bell peppers, zucchini, and cherry tomatoes, and toss with balsamic vinegar and Italian seasoning.
Thread the marinated chicken onto skewers, leaving a little space between each piece. Repeat with the shrimp and vegetables.
For the chicken skewers, brush with barbecue sauce before grilling.
Grill the chicken skewers for 10-12 minutes, turning occasionally, until cooked through. Grill the shrimp skewers for 5-7 minutes, turning once, until pink and opaque. Grill the vegetable skewers for 8-10 minutes, turning occasionally, until tender and slightly charred.
Remove skewers from the grill and let them rest for a few minutes before serving.