Preheat oven to 450°F. Toss together squash, onion, 3 tablespoons of the oil, 1 teaspoon of the salt, and 1/2 teaspoon of the pepper on rimmed baking sheet. Roast in preheated oven until squash is browned and tender, 20 to 25, rotating pan on rack after 15 minutes. Let stand until cool enough to handle.

Meanwhile, whisk together vinegar, lemon juice, honey, oregano, dill, and remaining 2 tablespoons oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a small bowl until thoroughly combined.

Combine chickpeas, olives, and walnuts in a large bowl; drizzle with dressing, and toss to combine. Add squash mixture and feta; toss lightly to combine. Sprinkle with parsley, and serve immediately.