How to Make It
Place chicken on a rimmed baking sheet; sprinkle evenly with 2 teaspoons salt, 2 teaspoons lemon zest, and 1 teaspoon black pepper. Refrigerate, uncovered, 8 hours or overnight.
Let chicken come to room temperature, about 1 hour. Preheat oven to 450°F. Add acorn squash to baking sheet; drizzle chicken and squash with olive oil. Sprinkle squash with 1 teaspoon salt and remaining 1 teaspoon black pepper. Tuck thyme sprigs around chicken and squash.
Bake in preheated oven until a thermometer inserted in thickest portion of chicken registers 165°F and squash is tender, about 35 minutes. Transfer chicken and squash to a platter. Discard thyme sprigs; reserve pan juices.
Heat butter in a small saucepan over medium, stirring occasionally, until browned and fragrant, about 3 minutes. Scrape pan juices from baking sheet into saucepan. Whisk in honey, 1/2 teaspoon sumac, remaining 2 teaspoons lemon zest, and remaining 1/4 teaspoon salt. Drizzle over chicken and squash. Sprinkle with Aleppo pepper, thyme leaves, and remaining 1/2 teaspoon sumac.
Look for sumac at your local Middle Eastern market or on Amazon.