01 - Set oven temperature to 400°F (204°C) and allow to preheat.
02 - Combine carrots, parsnips, and red onion in a large bowl; drizzle with 1 tablespoon olive oil and season with half of the kosher salt and black pepper. Toss until evenly coated.
03 - Spread prepared vegetables evenly onto a large rimmed baking sheet.
04 - Whisk together maple syrup, Dijon mustard, remaining olive oil, apple cider vinegar, garlic powder, and dried thyme in a small bowl until thoroughly combined.
05 - Pat chicken thighs dry and arrange atop vegetables. Sprinkle with remaining salt and pepper.
06 - Brush thighs generously with maple mustard sauce, ensuring even coverage.
07 - Transfer pan to oven and roast for 35–40 minutes until chicken skin is golden and internal temperature registers 165°F (74°C). Vegetables should be tender and caramelized.
08 - Remove from oven and allow chicken to rest 5 minutes before plating. Serve warm atop roasted vegetables.