Step 1

Preheat oven to 425°F. Toss together squash, onions, 1 tablespoon oil, 1 teaspoon salt, and 1/4 teaspoon black pepper on a baking sheet; spread in an even layer. Roast in preheated oven 25 minutes. Flip squash and onions; add peperoncini to baking sheet. Continue roasting until squash and onions are beginning to brown, about 15 minutes.

Step 2

Meanwhile, whisk together yogurt, vinegar, honey, oregano, remaining 6 tablespoons oil, remaining 1/2 teaspoon salt, and remaining 1/4 teaspoon black pepper in a small bowl.

Step 3

Transfer roasted squash mixture to a serving platter; drizzle with dressing. Garnish with grated cheese and sumac.