Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large bowl, combine the diced zucchini and corn. Drizzle with olive oil, garlic powder, salt, and pepper. Toss to coat evenly.
Spread the zucchini and corn mixture on the prepared baking sheet in a single layer. Roast in the preheated oven for 20-25 minutes, or until the zucchini is tender and slightly caramelized.
While the vegetables are roasting, prepare the Green Goddess dressing. In a medium bowl, whisk together Greek yogurt, mayonnaise, lemon juice, apple cider vinegar, minced garlic, chives, dill, salt, and pepper until smooth and well combined.
Once the zucchini and corn are done roasting, remove them from the oven and let them cool slightly.
In a large serving bowl, combine the roasted zucchini and corn, cherry tomatoes, red onion, basil, parsley, and avocado. Drizzle with the Green Goddess dressing and toss gently to combine.
Serve immediately or chill in the refrigerator for 30 minutes to allow the flavors to meld.