Roasted Squash Salad with Sumac and Italian Dressing

Name: Roasted Squash Salad with Sumac and Italian Dressing
Ingredients: 1 (24-ounce) acorn squash, halved lengthwise, seeded, and cut into 1-inch wedges; 3 small (6-ounce) red onions, cut into 1-inch wedges; 7 tablespoons extra-virgin olive oil, divided; 1 1/2 teaspoons kosher salt, divided; 1/2 teaspoon black pepper, divided; 9 jarred whole pickled peperoncini; 2 tablespoons plain whole-milk yogurt; 2 tablespoons red wine vinegar; 1 teaspoon honey; 1/2 teaspoon dried oregano; Freshly grated Parmigiano-Reggiano cheese and ground sumac, for garnish