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 the olive oil, garlic powder, oregano, salt, and black pepper. Add the chopped vegetables and toss until they are evenly coated with the marinade.
Thread the vegetables onto the skewers, alternating between different types for a colorful presentation.
Place the skewers on the grill and cook for about 10-12 minutes, turning occasionally, until the vegetables are tender and slightly charred.
Remove the skewers from the grill and let them cool for a few minutes before serving.