01 - Preheat oven to 425°F (220°C). Line a large rimmed baking sheet with parchment paper or foil for easier cleanup.
02 - Pat chicken thighs dry with paper towels. Season both sides with kosher salt and black pepper.
03 - In a large bowl, combine butternut squash, Brussels sprouts, carrots, and red onion. Toss with olive oil, dried thyme, rosemary, and ground cinnamon until evenly coated. Spread vegetables in an even layer on the prepared baking sheet.
04 - In a small bowl, whisk together honey, soy sauce or tamari, minced garlic, Dijon mustard, apple cider vinegar, and crushed red pepper flakes (if using).
05 - Nestle the seasoned chicken thighs, skin-side up, among the vegetables on the baking sheet.
06 - Brush half of the honey garlic sauce over the chicken thighs.
07 - Roast in the preheated oven for 25 minutes.
08 - Remove the pan from the oven. Brush the remaining honey garlic sauce over the chicken. Gently toss the vegetables. Return to oven and roast for an additional 15 minutes, or until the chicken is golden and cooked through (internal temperature should reach 165°F/74°C) and vegetables are tender.
09 - For extra caramelization, broil for 2 to 3 minutes if desired.
10 - Serve hot, spooning pan juices over the chicken and vegetables.