Preheat your grill to medium-high heat.
In a large bowl, combine the zucchini, yellow squash, red and yellow bell peppers, red onion, and cherry tomatoes. Drizzle with olive oil and season with salt, pepper, garlic powder, and dried oregano. Toss to coat the vegetables evenly.
Place the vegetables directly on the grill grates or use a grill basket. Grill for about 5-7 minutes, turning occasionally, until they are tender and have nice grill marks. Remove from the grill and let cool slightly.
In a small bowl, whisk together the balsamic vinegar, honey, and Dijon mustard until well combined.
Once the grilled vegetables are slightly cooled, transfer them to a serving bowl. Drizzle with the balsamic vinaigrette and toss gently to combine.
If desired, sprinkle with crumbled feta cheese and garnish with fresh basil leaves before serving.