Preheat your oven to 400°F (200°C). Pat the chicken thighs dry with paper towels and season them generously with salt and black pepper.
Heat olive oil in a large oven-proof skillet over medium-high heat until shimmering. Place the chicken thighs skin-side down and cook for about 5-7 minutes until the skin turns golden brown and crispy. Flip and cook another 3-4 minutes on the other side.
Add sliced onions around the chicken in the skillet, stirring gently to coat with the oil, and cook for 2-3 minutes until translucent and fragrant.
Stir in the minced garlic and chopped sage, cooking for about 30 seconds until aromatic.
Add the sweet potato chunks and sliced carrots into the skillet, stirring to combine and coat with the flavorful juices.
Transfer the entire skillet to the preheated oven and roast uncovered for 25-30 minutes, or until the chicken skin is crisp and the vegetables are tender.
Once cooked, remove the skillet from the oven and let it rest for 5 minutes. Check that the chicken is cooked through and juices run clear.
Serve the fall chicken with the roasted vegetables on a large platter or plates, spooning the flavorful pan juices over the top for added richness.