Preheat your oven to 400°F (200°C). Toss the chopped fall vegetables and sliced onions with olive oil, chopped sage, thyme, salt, and pepper in a large mixing bowl until evenly coated.
Spread the seasoned vegetables in an even layer in your baking dish or casserole pan. Place the dish in the oven and roast for 20 minutes until the vegetables start to soften and caramelize around the edges.
Meanwhile, season the chicken thighs or breasts with salt and pepper. Heat a skillet over medium-high heat and sear the chicken for 3-4 minutes per side until browned, then set aside.
Remove the roasted vegetables from the oven and nestle the seared chicken pieces among them. Return the dish to the oven and roast for an additional 20-25 minutes, until the chicken is cooked through and the vegetables are tender and caramelized.
Once cooked, transfer the casserole to a serving platter. Let it rest for a few minutes, allowing the juices to settle, then garnish with extra sage if desired.
Serve warm, enjoying the tender chicken coated in the flavorful roasted vegetables and herbs, with a golden, crispy top.
