If using wooden skewers, soak them in water for at least 30 minutes to prevent burning on the grill.
In a large bowl, combine the olive oil, garlic powder, oregano, salt, and black pepper. Mix well.
Add the zucchini, bell pepper, red onion, cherry tomatoes, and mushrooms to the bowl. Toss until all the vegetables are evenly coated with the marinade.
Preheat the grill to medium-high heat.
Thread the marinated vegetables onto the skewers, alternating between different types for a colorful presentation.
Place the skewers on the grill and cook for 10-12 minutes, turning occasionally, until the vegetables are tender and have nice grill marks.
Remove from the grill and let cool for a few minutes before serving.